Hepcidin, a urinary antimicrobial peptide synthesized in the liver Original paper

What was studied?

This study characterized hepcidin urinary antimicrobial peptide as a newly discovered, cysteine-rich human antimicrobial peptide that is synthesized in the liver and excreted into urine, and evaluated its structure, gene expression, and antimicrobial spectrum. The authors purified cationic peptides from pooled urine of healthy donors using cation exchange and reverse-phase HPLC, identified three processed hepcidin isoforms (Hepc20, Hepc22, Hepc25) by mass spectrometry and Edman sequencing, and used circular dichroism to infer a compact, disulfide-stabilized fold with β-turns/loops. They then cloned the corresponding cDNA and mapped the human genomic locus (chromosome 19), showing the peptide derives from an 84–amino acid prepropeptide with a signal peptide and probable propeptide convertase cleavage site. Antimicrobial function was tested via CFU-killing assays against bacterial strains and by germination and fungicidal assays against pathogenic Aspergillus spores, including assessment under higher-salt conditions that approximate physiologic environments.

Who was studied?

The human-derived component came from pooled urine of one to five healthy donors, used as the source material to purify native hepcidin peptides and estimate typical urinary concentrations (collectively ~10–30 mg/L). Tissue expression was assessed using commercial human organ mRNA Northern blots spanning fetal and adult tissues (including fetal and adult liver, kidney, blood leukocytes, and multiple organs), plus additional RNA prepared from normal human liver blocks. The antimicrobial targets were not human subjects but clinically relevant microbes used as experimental models: bacteria including Escherichia coli (ML35p), Staphylococcus aureus, Staphylococcus epidermidis, and group B Streptococcus; fungi including Candida albicans; and filamentous fungal clinical isolates of Aspergillus fumigatus and Aspergillus niger.

Most important findings

Hepcidin emerged as a liver-derived innate defense peptide with broad antimicrobial effects that are highly relevant for host–microbe interactions and for interpreting antimicrobial peptide signals in microbiome signature databases. Two predominant urinary forms, Hepc20 and Hepc25, are 20–25 amino acids long, contain 8 cysteines forming four intramolecular disulfide bonds, and circulate as small (2–3 kDa), highly structured peptides consistent with a “cystine-knot-like” antimicrobial scaffold. Hepcidin mRNA expression was strongly enriched in fetal and adult liver, with only trace signal in the heart and spinal cord, supporting hepatic origin despite urinary detection. Functionally, both Hepc20 and Hepc25 showed bactericidal activity at higher concentrations (notably against E. coli and S. epidermidis) and antifungal activity, including inhibition of Aspergillus spore germination; Hepc20 was consistently more potent than Hepc25 and could be fungicidal at the highest tested doses. A key translational nuance is that antimicrobial activity was salt-sensitive, being inhibited by added NaCl (100–150 mM), suggesting that compartment and ionic milieu (urine vs plasma/tissues) may determine in vivo impact.

Key implications

Clinically, this work reframes the liver as a direct producer of small antimicrobial peptides, positioning hepcidin urinary antimicrobial peptide as a plausible systemic-to-urinary effector linking hepatic immune sensing to downstream microbial control. For microbiome and infectious disease interpretation, the peptide’s selective activity (stronger versus some Gram-negative/Gram-positive targets and certain fungi, absent versus Pseudomonas) and marked salt sensitivity imply that hepcidin levels may correlate with microbial pressures differently across body sites and fluids. Although later research established hepcidin as a master iron-regulatory hormone, this foundational study highlights its antimicrobial phenotype, suggesting that shifts in hepcidin expression during inflammation, iron overload, or infection could reshape microbial ecology indirectly (via iron restriction) and directly (via peptide activity), making it a meaningful host-derived feature in microbiome-signature frameworks.

Citation

Park CH, Valore EV, Waring AJ, Ganz T. Hepcidin, a urinary antimicrobial peptide synthesized in the liver. J Biol Chem. 2001;276(11):7806-7810. doi:10.1074/jbc.M008922200