Effect of Hepcidin on Hypoxia-Induced Erythropoietin Production

Abstract 3219

The anemia of chronic disease (ACD) is the major etiology of the anemia observed in in chronically ill patients. ACD typically manifests itself as a hypoproliferative anemia accompanied by a low serum iron concentration despite adequate reticuloendothelial iron stores. In ACD, a slight shortening of red cell survival creates a demand for a small increase in red cell production by the bone marrow. The marrow cannot respond adequately to this demand due to impaired erythropoiesis and impaired mobilization of reticuloendothelial system iron stores. Increased production of the iron regulatory peptide hepcidin has been proposed as the primary factor resulting in ACD. Hepcidin has also been reported to decrease erythroid colony formation in vitro under conditions of restrictive Epo concentration. A blunted erythropoietin (Epo) response to anemia is a characteristic feature of ACD. If hepcidin is the major factor responsible for ACD, then it should also contribute to the impaired Epo production observed in this syndrome.

The effect of hepcidin on hypoxia-induced Epo production was evaluated in HepG2 cells exposed to 5% oxygen for 24 hr. 24 hr exposure to hepcidin during hypoxia at the concentrations studied (up to 100 ng/mL) had no adverse effect on HepG2 cell viability compared to controls as evaluated by cell number and Trypan blue exclusion or on cellular synthetic function as measured by alpha fetoprotein. Epo production (whether measured by Western blot or by ELISA) was increased by hypoxia; however, this increase was blunted by the addition of hepcidin to the incubation medium. Impairment of hypoxia-induced Epo production by hepcidin showed a dose-response relationship. The addition of iron-replete transferrin to the incubation mixture did not significantly alter hepcidin effects, suggesting that these effects do not primarily reflect changes in iron availability.

In order to evaluate mechanisms by which hepcidin might decrease Epo production, effects of hepcidin 0–100 ng/mL on hypoxia-inducible factor (HIF)-1α protein expression were evaluated in HepG2 cells (HIF expression was normalized to actin expression). The increment in HIF-1α caused by hypoxia was decreased by hepcidin in a dose-dependent manner. The ratio of Epo to HIF was not altered by hepcidin, suggesting that hepcidin effects on HIF may be the mechanism of its effects on Epo production.

In conclusion, hepcidin appears to blunt the increment in Epo production induced by hypoxia in vitro. This mechanism does not appear to be reversible by exposure to increased quantities of transferrin-bound iron. This finding is consistent with a role for hepcidin in the impaired Epo production of ACD independent of its effects on iron flux.