What Is Hepcidin? The Iron Hormone Found as an Antibiotic

Peptide reference

Hepcidin is a 25-amino-acid liver peptide that sets how much iron the body is allowed to move — and it was characterised twice, by two laboratories that both thought they had found an antibiotic. Neither original paper mentions iron. The connection came a few months later, from a mouse engineered to study sugar metabolism that unexpectedly rusted.

What is hepcidin?

Hepcidin is the master regulator of systemic iron. The HAMP gene at 19q13.12 encodes an 84-residue precursor; processing removes a 24-residue signal peptide and a propeptide to leave the mature hormone, hepcidin-25, at residues 60–84. Shorter 22- and 20-residue forms exist, produced by trimming from the N-terminus, and are generally regarded as far less active in iron regulation.

For a peptide this small it is unusually constrained. Eight cysteines form four disulfide bonds, locking a hairpin that is essentially rigid. That density of crosslinking is what made hepcidin hard to characterise — and, as it turned out, easy to get wrong. The connectivity published in 2002 included an unusual vicinal bridge at the turn of the hairpin; a 2009 paper titled “Hepcidin revisited” used multiple independent techniques to demonstrate a different pattern altogether. UniProt now flags the 2002 assignment explicitly as preliminary. A 25-residue peptide took nine years and two structural revisions to settle.

Discovered as an antibiotic, twice

In September 2000, Krause and colleagues reported LEAP-1 — liver-expressed antimicrobial peptide — isolated from human blood ultrafiltrate by a mass-spectrometric screen for cysteine-rich peptides, and active in radial diffusion assays against Gram-positive and Gram-negative bacteria and against Saccharomyces cerevisiae. Three months later, Park, Ganz and colleagues independently isolated the same peptide from human urine in three N-terminally truncated forms and named it hepcidin “because of its origin in the liver and its antimicrobial properties.” They suggested it might be a vertebrate counterpart of the antimicrobial peptides made in the fat body of insects. Neither abstract contains the word iron.

The link arrived in July 2001 from an entirely different direction. A French group had knocked out Usf2, a transcription factor, to study glucose-dependent gene regulation in the liver. They reported what they called “a peculiar phenotype”: the mice progressively developed multivisceral iron overload, with plasma iron exceeding transferrin binding capacity and, strikingly, lower splenic iron than controls. The hepcidin gene sits beside Usf2 and had been silenced along with it. The authors concluded that a complete defect in hepcidin expression was responsible.

Hepcidin’s antimicrobial activity is genuine but modest, and the name now records a hypothesis rather than the peptide’s main job. The two ideas are not unrelated, though: withholding iron from plasma is itself an antimicrobial strategy, since most pathogens need iron to grow. See antimicrobial peptides explained for the wider family hepcidin was originally filed under.

How hepcidin works: one hormone, one transporter

Hepcidin has a single known molecular target: ferroportin, encoded by SLC40A1 at 2q32.2, which moves ferrous iron out of cells. Ferroportin sits on the basolateral membrane of intestinal enterocytes, on macrophages recycling iron from senescent red cells, and on hepatocytes storing it. Essentially every route by which iron enters plasma runs through it. Control that transporter and you control the whole system.

The 2004 model from Nemeth, Ganz, Kaplan and colleagues in Science was elegantly simple: hepcidin binds ferroportin, ferroportin is internalised and degraded, cellular iron export falls. Iron regulates hepcidin secretion, hepcidin regulates surface ferroportin, and the loop closes.

That model turned out to be incomplete rather than wrong. A 2018 structure-function study showed hepcidin can also simply occlude the transporter, blocking iron export with no endocytosis at all — demonstrated in cells expressing an endocytosis-defective ferroportin mutant, in Xenopus oocytes, and, decisively, in mature human red blood cells, which cannot endocytose anything. A 2020 cryo-electron microscopy structure confirmed it: hepcidin binds ferroportin in an outward-open conformation and “completely occludes the iron efflux pathway.”

The same structure revealed a neat piece of logic. Hepcidin’s affinity for ferroportin rises about 80-fold in the presence of iron, and the peptide’s C-terminus contacts the bound metal directly. In effect only loaded transporters are efficiently marked for shutdown — the hormone preferentially disables the molecules actually doing the exporting.

What turns hepcidin up and down

Four inputs dominate, and they pull in different directions:

• Iron raises it, through bone morphogenetic protein 6 signalling to SMAD transcription factors, with hemojuvelin as a co-receptor. Two groups reported back to back in 2009 that Bmp6-null mice have low hepcidin and tissue iron overload — a phenotype resembling hereditary haemochromatosis. Notably, those mice still raise hepcidin normally in response to inflammation, so the two pathways are separable.
• Inflammation raises it, via interleukin-6 and STAT3. A 2004 human and mouse study concluded that IL-6 is “the necessary and sufficient cytokine for the induction of hepcidin during inflammation” and that this axis is responsible for the hypoferraemia of inflammation.
• Erythropoietic drive lowers it. In 2014 the Ganz laboratory identified erythroferrone, a hormone released by erythroblasts in response to erythropoietin that suppresses hepcidin. Erythroferrone-deficient mice fail to suppress hepcidin promptly after haemorrhage and recover from blood loss more slowly.
• Hypoxia and anaemia lower it, largely through that same erythropoietin-to-erythroferrone route. Work on the VHL/HIF pathway showed coordinate downregulation of hepcidin alongside upregulation of erythropoietin and ferroportin; whether HIF also represses the HAMP promoter directly remains contested.

Hemojuvelin is itself regulated: the liver protease TMPRSS6 cleaves it from the cell surface, which damps BMP signalling and lowers hepcidin. That relationship becomes the basis for two drug programmes further down.

Why the direction is the opposite of what people assume

Hepcidin is often introduced as “the iron hormone,” which invites the wrong inference. It does not raise iron; it withdraws it from circulation. High hepcidin means ferroportin is shut, iron is retained inside enterocytes and macrophages, and serum iron falls. Low hepcidin means ferroportin stays open and iron floods into plasma and then into parenchymal tissue.

That single sign flip explains two families of disease. Hereditary haemochromatosis — whether from HFE, HJV, TFR2 or HAMP mutations — is fundamentally a hepcidin-deficiency state; in juvenile haemochromatosis caused by hemojuvelin mutations, urinary hepcidin was measured as depressed, which is what told the field that hemojuvelin modulates hepcidin rather than being its receptor. At the other pole, anaemia of inflammation is a hepcidin-excess state in which, as a 2019 Blood review puts it, hepcidin and inflammatory cytokines “block intestinal iron absorption and cause iron retention in reticuloendothelial cells, resulting in iron-restricted erythropoiesis.” The stores are full; the iron simply cannot get out.

A third disease, iron-refractory iron deficiency anaemia, makes the logic unmistakable. Loss-of-function mutations in TMPRSS6 remove the brake on hepcidin, hepcidin runs high, and the result is an iron-deficiency anaemia that oral iron cannot correct — the “refractory” in the name is a direct readout of hepcidin biology.

Why nobody orders a hepcidin level

Given how central it is, hepcidin measurement ought to be routine. It is not, and the reason is unglamorous: the assays do not agree with each other. The first international round robin, published in 2009, found that “the absolute hepcidin concentrations differed widely between methods.” A second round in 2012 across 21 methods reported that results are “not harmonized” and that “different numeric results are obtained for the same clinical sample” — and, awkwardly, that for most methods samples spiked with synthetic hepcidin-25 were not commutable with native samples.

A 2019 standardisation effort put numbers on it: inter-assay coefficients of variation of 42.1% and 52.8% without harmonisation, falling to 11.0% and 19.1% after calibration against a reference material. A 2016 review concluded that “a gold standard is still lacking,” while pointing to real near-term uses — diagnosing iron-refractory iron deficiency anaemia, and guiding safe iron supplementation in settings with a high infection burden. For that reason no reference interval is quoted on this page: any single range would be method-specific.

Drugging the pathway

The furthest-advanced agent is rusfertide, an injected hepcidin mimetic. Its phase 3 VERIFY trial randomised 293 patients with polycythaemia vera, a disease of overproduced red cells in which the standard management is repeated therapeutic phlebotomy. Response was defined as absence of phlebotomy eligibility during weeks 20 to 32. Reported at ASCO in 2025, 76.9% of rusfertide patients responded versus 32.9% on placebo (p<0.0001); the mean number of phlebotomies over 32 weeks was 0.5 versus 1.8, and 62.6% versus 14.4% held haematocrit below 45% throughout. Injection-site reactions (55.9% vs 32.9%) and anaemia (15.9% vs 4.1%) were the main tolerability findings. An imbalance in new malignancies — one on rusfertide, seven on placebo — is an observation in a 32-week window, not an anticancer signal.

An FDA new drug application was accepted with priority review in March 2026, with a goal date in the third quarter of the year. As of 28 August 2026, searches of Drugs@FDA and DailyMed return no approved application and no US prescribing label for rusfertide. That is a two-day-old snapshot of two databases, so it describes US registry status rather than global approval.

The rest of the field is thinner. Vamifeport, an oral ferroportin inhibitor, completed phase 2 studies in beta-thalassaemia and sickle cell disease, had a third withdrawn for “strategic reasons,” and has reappeared under CSL Behring in a phase 2 haemochromatosis trial recruiting since January 2026. Two programmes raise endogenous hepcidin by silencing TMPRSS6: sapablursen, an antisense oligonucleotide whose thalassaemia study was terminated because efficacy “did not meet Ionis’ minimum target product profile,” but which is now in a phase 3 polycythaemia vera trial recruiting from 2026; and SLN124, a small interfering RNA in phase 1/2.

Attempts to go the other way — blocking hepcidin to release trapped iron in anaemia of inflammation — have gone nowhere so far. The anti-hepcidin antibody LY2787106 produced dose-dependent rises in serum iron and transferrin saturation that peaked within 24 hours and returned to baseline by day 8; no phase 2 was ever registered. The anti-hepcidin aptamer lexaptepid pegol raised iron by about 67% eight hours after infusion in healthy subjects and completed four trials, with nothing registered since 2015. Neither programme has a published discontinuation notice; they simply stopped. Antibody approaches to peptide targets carry their own complications — see anti-drug antibodies.

Handling and measurement notes

Hepcidin appears in most laboratories as an analyte or a synthetic reference standard rather than as a therapeutic. The points below are general to constrained, multi-disulfide peptides.

• The fold is the molecule. Four disulfide bonds mean reducing conditions, extremes of pH and thiol-containing buffers can inactivate the peptide while leaving its mass nearly unchanged. Identity confirmed by mass alone is not identity confirmed.
• Adsorption is real for small cationic peptides. The hepcidin assay literature repeatedly notes that spiked synthetic material is not commutable with native samples — a reminder that container surfaces and carrier proteins change measured concentrations. Solubility and diluent choice covers the practical side.
• Concentration is arithmetic, not a label. To convert a stated mass and a volume into a working concentration, use the reconstitution calculator; the concentration converter handles the reverse direction. General handling is covered in how to reconstitute peptides and sterile technique.
• Peptide hormones are short-lived by default. Rusfertide is an engineered mimetic rather than the native peptide, for the reasons set out in half-life extension strategies.

Frequently asked questions

Does high hepcidin mean high iron?

No — the opposite. High hepcidin closes ferroportin, so iron stays locked inside intestinal cells and macrophages and serum iron falls. Anaemia of inflammation is a high-hepcidin state with full iron stores that the marrow cannot reach. Hereditary haemochromatosis, by contrast, is a low-hepcidin state.

Why is hepcidin not a routine blood test?

Because different assays return materially different numbers for the same sample. Published inter-assay coefficients of variation reached 42–53% before harmonisation efforts, and even after calibration against a reference material they sat at 11–19%. Reviewers in the field still describe the absence of a gold standard as the limiting problem.

Is hepcidin an antimicrobial peptide or a hormone?

Historically both. It was named and published twice as an antimicrobial peptide before its iron-regulatory role was found, and it does have measurable antimicrobial activity. Its physiologically dominant function is iron regulation — though restricting plasma iron is itself a defence against iron-dependent pathogens, so the two roles are less separate than the naming suggests.

Is there an approved hepcidin drug?

Not in the United States as of late August 2026. Rusfertide, a hepcidin mimetic, met its primary endpoint in a phase 3 polycythaemia vera trial and has an FDA new drug application under priority review, but neither Drugs@FDA nor DailyMed lists an approved application or a prescribing label for it, or for any other hepcidin- or ferroportin-directed agent.

Informational only — not medical advice · 21+. Consult a qualified healthcare professional about any medical question.