Mark Westerman

Immunoassay for human serum hepcidin

We developed and validated the first serum enzyme-linked immunosorbent assay for hepcidin, the principal iron-regulatory hormone that has been very difficult to measure. In healthy volunteers, the 5% to 95% range of hepcidin concentrations was 29 to 254 ng/mL in men (n = 65) and 17 to 286 ng/mL in women (n = 49), with median concentrations 112 versus 65 (P < .001). The lower limit of detection was 5 ng/mL. Serum hepcidin concentrations in 24 healthy subjects correlated well with their urinary hepcidin (r = 0.82). Serum hepcidin appropriately correlated with serum ferritin (r = 0.63), reflecting the regulation of both proteins by iron stores. Healthy volunteers showed a diurnal increase of serum hepcidin at noon and 8 pm compared with 8 am, and a transient rise of serum hepcidin in response to iron ingestion. Expected alterations in hepcidin levels were observed in a variety of clinical conditions associated with iron disturbances. Serum hepcidin concentrations were undetectable or low in patients with iron deficiency anemia (ferritin < 10 ng/mL), iron-depleted HFE hemochromatosis, and juvenile hemochromatosis. Serum hepcidin concentrations were high in patients with inflammation (C-reactive protein > 10 mg/dL), multiple myeloma, or chronic kidney disease. The new serum hepcidin enzyme-linked immunosorbent assay yields accurate and reproducible measurements that appropriately reflect physiologic, pathologic, and genetic influences, and is informative about the etiology of iron disorders.

Discovery and Characterization of Two Isoforms of Moronecidin, a Novel Antimicrobial Peptide from Hybrid Striped Bass

We isolated a novel 22-residue, C-terminally amidated antimicrobial peptide, moronecidin, from the skin and gill of hybrid striped bass. Two isoforms, differing by only one amino acid, are derived from each parental species, white bass (Morone chrysops) and striped bass (Morone saxatilis). Molecular masses (2543 and 2571 Da), amino acid sequences (FFHHIFRGIVHVGKTIH(K/R)LVTGT), cDNA, and genomic DNA sequences were determined for each isoform. A predicted 79-residue moronecidin prepropeptide consists of three domains: a signal peptide (22 amino acids), a mature peptide (22 amino acids), and a C-terminal prodomain (35 amino acids). The synthetic, amidated white bass moronecidin exhibited broad spectrum antimicrobial activity that was retained at high salt concentration. An α-helical structure was confirmed by circular dichroism spectroscopy. The moronecidin gene consists of three introns and four exons. Peptide sequence and gene organization were similar to pleurocidin, an antimicrobial peptide from winter flounder. A TATA box and several consensus-binding motifs for transcription factors were found in the region 5′ to the transcriptional start site. Moronecidin gene expression was detected in gill, skin, intestine, spleen, anterior kidney, and blood cells by kinetic reverse transcription (RT)-PCR. Thus, moronecidin is a new α-helical, broad spectrum antimicrobial peptide isolated from the skin and gills of hybrid striped bass.

Hepcidin - A potential novel biomarker for iron status in chronic kidney disease

BACKGROUND AND OBJECTIVES Hepcidin is a key regulator of iron homeostasis, but its study in the setting of chronic kidney disease (CKD) has been hampered by the lack of validated serum assays. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS This study reports the first measurements of bioactive serum hepcidin using a novel competitive ELISA in 48 pediatric (PCKD2-4) and 32 adult (ACKD2-4) patients with stages 2 to 4 CKD along with 26 pediatric patients with stage 5 CKD (PCKD5D) on peritoneal dialysis. RESULTS When compared with their respective controls (pediatric median = 25.3 ng/ml, adult = 72.9 ng/ml), hepcidin was significantly increased in PCKD2-4 (127.3 ng/ml), ACKD2-4 (269.9 ng/ml), and PCKD5D (652.4 ng/ml). Multivariate regression analysis was used to assess the relationship between hepcidin and indicators of anemia, iron status, inflammation, and renal function. In PCKD2-4 (R(2) = 0.57), only ferritin correlated with hepcidin. In ACKD2-4 (R(2) = 0.78), ferritin and soluble transferrin receptor were associated with hepcidin, whereas GFR was inversely correlated. In PCKD5D (R(2) = 0.52), percent iron saturation and ferritin were predictors of hepcidin. In a multivariate analysis that incorporated all three groups (R(2) = 0.6), hepcidin was predicted by ferritin, C-reactive protein, and whether the patient had stage 5D versus stages 2 to 4 CKD. CONCLUSIONS These findings suggest that increased hepcidin across the spectrum of CKD may contribute to abnormal iron regulation and erythropoiesis and may be a novel biomarker of iron status and erythropoietin resistance.

A mutation in the TMPRSS6 gene, encoding a transmembrane serine protease that suppresses hepcidin production, in familial iron deficiency anemia refractory to oral iron

Previous studies have described a familial syndrome characterized by iron malabsorption, hypoferremia, and microcytic anemia that did not respond to oral iron and responded only partly to parenteral iron. In this work, Melis and coworkers studied a Sardinian family with this inherited condition. They found a homozygous causal mutation in the TMPRSS6 gene in affected members, who had inappropriately elevated levels of serum and urinary hepcidin. See related perspective article on page 1441. Background Hepcidin plays a key role in body iron metabolism by preventing the release of iron from macrophages and intestinal cells. Defective hepcidin synthesis causes iron loading, while overproduction results in defective reticuloendothelial iron release and iron absorption. Design and Methods We studied a Sardinian family in which microcytic anemia due to defective iron absorption and utilization is inherited as a recessive character. Five members showed iron deficiency anemia that was not responsive to oral iron and only partially responsive to parenteral iron administration. To investigate the involvement of known genes implicated in iron metabolism we carried out linkage analysis with microsatellite markers mapping close to these genes. Afterwards, a genome-wide search was performed. Results No linkage was found between the phenotype of the patients and several known human genes involved in iron metabolism (DMT1, TF, TFRC, ZIRTL, HAMP, HJV). Genome-wide scanning by microsatellites and single nucleotide polymorphisms showed a multipoint LOD score of 5.6 on chromosome 22q12.3–13.1, where the matriptase-2 (also known as transmembrane protease, serine 6 or TMPRSS6) gene is located. Its murine counterpart (Tmprss6) has recently been found to be an essential component of a pathway that detects iron deficiency and suppresses hepcidin production. Sequencing analysis of TMPRSS6 revealed a homozygous causal mutation, predicting a splicing error and a truncated TMPRSS6 protein in affected members. Homozygous subjects had inappropriately elevated levels of serum and urinary hepcidin. Conclusions The findings of this study suggest that the observed TMPRSS6 mutation leads to overproduction of hepcidin and, in turn, to defective iron absorption and utilization. More generally, they confirm in humans the inhibitory effect of matriptase-2 on hepcidin synthesis already demonstrated in mice.

Testosterone Suppresses Hepcidin in Men: A Potential Mechanism for Testosterone-Induced Erythrocytosis

CONTEXT The mechanisms by which testosterone increases hemoglobin and hematocrit are unknown. OBJECTIVE The aim was to test the hypothesis that testosterone-induced increase in hematocrit is associated with suppression of the iron regulatory peptide hepcidin. PARTICIPANTS Healthy younger men (ages 19-35 yr; n = 53) and older men (ages 59-75 yr; n = 56) were studied. METHODS Weekly doses of testosterone enanthate (25, 50, 125, 300, and 600 mg) were administered over 20 wk, whereas endogenous testosterone was suppressed by monthly GnRH agonist administration. Blood and serum parameters from each individual were measured at wk 0, 1, 2, 4, 8, and 20. Longitudinal analyses were performed to examine the relationship between hepcidin, hemoglobin, hematocrit, and testosterone while controlling for potential confounders. RESULTS High levels of testosterone markedly suppressed serum hepcidin within 1 wk. Hepcidin suppression in response to testosterone administration was dose-dependent in older men and more pronounced than in young men, and this corresponded to a greater rise in hemoglobin in older men. Serum hepcidin levels at 4 and 8 wk were predictive of change in hematocrit from baseline to peak levels. CONCLUSION Testosterone administration is associated with suppression of serum hepcidin. Greater increases in hematocrit in older men during testosterone therapy are related to greater suppression of hepcidin.

Streptococcus iniae Phosphoglucomutase Is a Virulence Factor and a Target for Vaccine Development

ABSTRACT Streptococcus iniae represents a major health and economic problem in fish species worldwide. Random Tn917 mutagenesis and high-throughput screening in a hybrid striped bass (HSB) model of meningoencephalitis identified attenuated S. iniae mutants. The Tn917 insertion in one mutant disrupted an S. iniae homologue of a phosphoglucomutase (pgm) gene. Electron microscopy revealed a decrease in capsule thickness and cell wall rigidity, with ΔPGM mutant cells reaching sizes ∼3-fold larger than those of the wild type (WT). The ΔPGM mutant was cleared more rapidly in HSB blood and was more sensitive to killing by cationic antimicrobial peptides including moronecidin from HSB. In vivo, the ΔPGM mutant was severely attenuated in HSB, as intraperitoneal challenge with 1,000 times the WT lethal dose produced only 2.5% mortality. Reintroduction of an intact copy of the S. iniae pgm gene on a plasmid vector restored antimicrobial peptide resistance and virulence to the ΔPGM mutant. In analysis of the aborted infectious process, we found that ΔPGM mutant organisms initially disseminated to the blood, brain, and spleen but were eliminated by 24 h without end organ damage. Ninety to 100% of fish injected with the ΔPGM mutant and later challenged with a lethal dose of WT S. iniae survived. We conclude that the pgm gene is required for virulence in S. iniae, playing a role in normal cell wall morphology, surface capsule expression, and resistance to innate immune clearance mechanisms. An S. iniae ΔPGM mutant is able to stimulate a protective immune response and may have value as a live attenuated vaccine for aquaculture.

Suppression of Iron-Regulatory Hepcidin by Vitamin D

The antibacterial protein hepcidin regulates the absorption, tissue distribution, and extracellular concentration of iron by suppressing ferroportin-mediated export of cellular iron. In CKD, elevated hepcidin and vitamin D deficiency are associated with anemia. Therefore, we explored a possible role for vitamin D in iron homeostasis. Treatment of cultured hepatocytes or monocytes with prohormone 25-hydroxyvitamin D or active 1,25-dihydroxyvitamin D decreased expression of hepcidin mRNA by 0.5-fold, contrasting the stimulatory effect of 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D on related antibacterial proteins such as cathelicidin. Promoter-reporter and chromatin immunoprecipitation analyses indicated that direct transcriptional suppression of hepcidin gene (HAMP) expression mediated by 1,25-dihydroxyvitamin D binding to the vitamin D receptor caused the decrease in hepcidin mRNA levels. Suppression of HAMP expression was associated with a concomitant increase in expression of the cellular target for hepcidin, ferroportin protein, and decreased expression of the intracellular iron marker ferritin. In a pilot study with healthy volunteers, supplementation with a single oral dose of vitamin D (100,000 IU vitamin D2) increased serum levels of 25D-hydroxyvitamin D from 27±2 ng/ml before supplementation to 44±3 ng/ml after supplementation (P<0.001). This response was associated with a 34% decrease in circulating levels of hepcidin within 24 hours of vitamin D supplementation (P<0.05). These data show that vitamin D is a potent regulator of the hepcidin-ferroportin axis in humans and highlight a potential new strategy for the management of anemia in patients with low vitamin D and/or CKD.

Modulation of hepcidin production during hypoxia-induced erythropoiesis in humans in vivo: data from the HIGHCARE project

Iron is tightly connected to oxygen homeostasis and erythropoiesis. Our aim was to better understand how hypoxia regulates iron acquisition for erythropoiesis in humans, a topic relevant to common hypoxia-related disorders. Forty-seven healthy volunteers participated in the HIGHCARE project. Blood samples were collected at sea level and after acute and chronic exposure to high altitude (3400-5400 m above sea level). We investigated the modifications in hematocrit, serum iron indices, erythropoietin, markers of erythropoietic activity, interleukin-6, and serum hepcidin. Hepcidin decreased within 40 hours after acute hypoxia exposure (P < .05) at 3400 m, reaching the lowest level at 5400 m (80% reduction). Erythropoietin significantly increased (P < .001) within 16 hours after hypoxia exposure followed by a marked erythropoietic response supported by the increased iron supply. Growth differentiation factor-15 progressively increased during the study period. Serum ferritin showed a very rapid decrease, suggesting the existence of hypoxia-dependent mechanism(s) regulating storage iron mobilization. The strong correlation between serum ferritin and hepcidin at each point during the study indicates that iron itself or the kinetics of iron use in response to hypoxia may signal hepcidin down-regulation. The combined and significant changes in other variables probably contribute to the suppression of hepcidin in this setting.

Serum hepcidin is significantly associated with iron absorption from food and supplemental sources in healthy young women

BACKGROUND Hepcidin is a key regulator of iron homeostasis, but to date no studies have examined the effect of hepcidin on iron absorption in humans. OBJECTIVE Our objective was to assess relations between both serum hepcidin and serum prohepcidin with nonheme-iron absorption in the presence and absence of food with the use of dual stable-iron-isotope techniques. DESIGN The study group included 18 healthy nonpregnant women. Women received in random order a supplemental iron source (7.6 mg FeSO4 providing 0.9 mg 58Fe as FeSO4) and 6.8 mg 57Fe ferrous sulfate tracer administered with a nonheme food source [orange-fleshed sweet potato (OFSP): 1.4 mg native Fe]. Iron absorption was determined by analyzing blood samples taken 14 d after dosing with the use of magnetic sector thermal ionization mass spectrometry. Serum hepcidin was assessed by a new competitive serum enzyme-linked immunosorbent assay (ELISA) specific for the refolded, mature 25-amino acid form, and serum prohepcidin was assessed by an ELISA specific for amino acids 28-47 of the hepcidin prohormone. RESULTS In these women, iron absorption averaged 14.71 +/- 10.7% from the supplemental iron compared with 3.63 +/- 6.5% from the OFSP. Absorption of nonheme iron assessed in the presence (P = 0.038) and absence (P = 0.0296) of food was significantly associated with serum hepcidin but was not significantly related to serum prohepcidin. CONCLUSION Serum hepcidin, but not prohepcidin, was inversely associated with iron absorption from supplemental and food-based nonheme-iron sources in iron-replete healthy women.

Maternal serum hepcidin is low at term and independent of cord blood iron status.

Objectives:  Hepcidin is the key regulator of iron homeostasis. The aims of this study were to determine serum hepcidin concentrations and reference ranges in pregnant women and cord blood of newborns at term and to evaluate the associations between hepcidin concentrations and iron status parameters.