Hepcidin and its role in regulating systemic iron metabolism.

Maintenance of stable extracellular iron concentrations requires the coordinate regulation of iron transport into plasma from dietary sources in the duodenum, from recycled senescent red cells in macrophages and from storage in hepatocytes. Moreover, during fetal development, the iron requirements of the fetus must be matched by the transport of maternal iron across the placenta. Hepcidin is a 25-amino acid disulfide-rich peptide synthesized in the liver that acts as a systemic iron-regulatory hormone by regulating iron transport from iron-exporting tissues into plasma. Hepcidin inhibits the cellular efflux of iron by binding to, and inducing the degradation of, ferroportin, the sole iron exporter in iron-transporting cells. In turn, hepcidin synthesis is increased by iron loading and decreased by anemia and hypoxia. Additionally, hepcidin synthesis is greatly increased during inflammation, trapping iron in macrophages, decreasing plasma iron concentrations and causing iron-restricted erythropoiesis characteristic of anemia of inflammation (anemia of chronic disease). Recent studies indicate that hepcidin deficiency underlies most known forms of hereditary hemochromatosis. This implies that, with the exception of very rare mutations that affect the hepcidin gene itself or modify ferroportin to make it less responsive to hepcidin, hemochromatosis genes encode molecules that regulate hepcidin synthesis. The central involvement of hepcidin in iron regulation and its pathologies should make the eventual hepcidin assay useful for the diagnosis of iron disorders and the monitoring of their treatments. The development of hepcidin agonists and antagonists may provide useful therapeutics for the treatment of iron disorders.