Hepcidin-Ferroportin Interactions: Targeting by Rational Drug Design

The interaction between the iron regulatory peptide hormone hepcidin and the iron channel ferroportin is central to iron homeostasis, and alterations in their interaction are responsible for common iron disorders. In this study, we used structure-function analysis to determine the critical aspects of the hepcidin-ferroportin interaction and then demonstrated that the approach could be useful for the development of hepcidin agonists or antagonists.;First we analyzed the physicochemical characteristics of the hepcidin-ferroportin interaction, and determined that hepcidin binding to ferroportin is both temperature and pH dependent. Additionally, we showed that bound hepcidin is not recycled but is internalized and degraded with ferroportin in lysosomes and proteasomes. We used PET/CT animal imaging to confirm that hepcidin is cleared from the circulation by both receptor-mediated endocytosis in target organs and renal filtration and excretion.;Next, we performed comprehensive structural modifications of the hepcidin molecule, site directed mutagenesis of the hepcidin-binding loop of ferroportin, and RosettaDock computer modeling of the ligand-receptor interface. These studies revealed that the key amino acid side chain contacts that are critical for the hepcidin-ferroportin interaction and suggested the possibility that disulfide exchange occurs between the ligand and its receptor. Based on these findings, we undertook the rational design of hepcidin agonists, "mini-hepcidins". The small synthetic peptides replicated the effect of native hepcidin on serum iron in mice, with potency equal to or greater than that of the native hormone. The peptides were active both when administered by intraperitoneal injection and orally. These lead compounds have potential for further development as drugs for the treatment of iron overload in hereditary hemochromatosis and thalassemic disorders.