Liver Hepcidin Research Articles

Dual function of fish hepcidin: Response to experimental iron overload and bacterial infection in sea bass ( Dicentrarchus labrax)

The role of hepcidin in iron metabolism regulation and bacterial infection has been the focus of recent attention. However, in spite of the growing number of hepcidin genes known from different organisms, little is known about its putative dual function in fish. The aim of this study was to characterize the sea bass hepcidin gene and to study its role in iron metabolism and infection. The novel sea bass hepcidin gene was found to be organized into two introns and three exons with several copies present in the genome. The transcript showed a constitutive low basal expression being mainly expressed in liver and encoding a putative 85 residues long peptide. Fish were submitted either to iron status modulation or bacterial infection and the hepcidin transcript levels were analysed along with a number of other parameters. Liver hepcidin expression was found to increase in both the iron-overloaded and infected fish, while in the iron-deficient fish no alteration in expression levels was detected. These results point to the evolutionary conservation of hepcidin's dual functions.

Liver Hepcidin mRNA Is down Regulated at High Liver Iron Burdens and up Regulated in HCV Infection in Thalassaemia.

Rationale. Hepcidin is an important negative regulator of iron absorption from the gut and iron release from macrophages. Synthesis is increased by inflammation and decreased in iron deficiency. Iron overload conditions might be predicted to up-regulate hepcidin synthesis, thereby decreasing dietary iron absorption. However in adult onset herediditary hemochromatosis, there is paradoxical down regulation of liver hepcidin mRNA (Bridle et al.,Lancet 2003). Urinary hepcidin is decreased thalassaemia major (Papanikolaou et al., Blood 2005) but expression of mRNA has not been described. However, hepcidin mRNA may be increased in iron overloaded in patients with chronic HCV infection (Aoki, et al., J Clin Gasteroenterol 2005).Methodology. mRNA was extracted on 20 liver biopsies from thalassaemia patients and RT PCR performed from cDNA as described by Leung et al., Blood 2005. 14 biopsies were obtained from thalassaemia major (TM) patients on regular transfusion programmes and the remaining 6 from thalassaemia intermedia (TI) patients, 2 of whom were not currently receiving transfusion, 3 were on exchange transfusion regimes and one was on 6–8 weekly top up transfusions. All samples were calculated as the hepcidin/actin ratio and were measured simultaneously with liver biopsies obtained from healthy control subjects at the time of surgery. Hepcidin mRNA was then expressed relative to control values from normal liver tissue in healthy control subjects.Results. Mean hepcidin mRNA was significantly lower in patients with liver iron concentrations >10mg/g/dw compared to those with lower burdens (85 vs 131%, p=0.05). Hepcidin mRNA did not vary significantly with anaemia, with ferritin > 3000ng/ml or <1500ng/ml (p=0.99). Hepcidin mRNA was not significantly different between the 2 thalassemia groups; TI (123 ± 47%) compared to (110 ± 73%)TM. 3 patients with high transaminase levels (>80 iu/ml) all had low hepcidin mRNA levels (77 ± 16 %) and increased levels of fibrosis compared to those with lower transaminase levels (106 ± 55%) and only mild fibrosis. 4 patients who were HCV antibody positive but with only modestly elevated transaminase levels (<160iu/ml) and mild/moderate fibrosis had raised hepcidin mRNA (163 + 70 %) p=0.02. There was no difference in the HCV positive and HCV negative groups for ferritin (2530 ng/ml: 2483 ng/ml), ALT (61 iu/l :53 iu/l) or liver iron (7.5 mg/g/dw versus 8.2 mg/g/dw).Conclusions. This suggests a critical level of iron burden (LIC) above which hepcidin expression becomes dysregulated, failing to increase with further elevations in the iron burden and paradoxically decreases. This could lead to inappropriately high iron absorption in heavily iron-loaded patients. Of other interacting factors affecting hepcidin synthesis, this study suggests that active HCV may increase hepcidin synthesis.

Mechanisms Regulating Iron Absorption over a Wide Range of Dietary Iron Content in the Mouse.

Dietary iron absorption by enterocytes is mediated by a ferrous transporter (DMT1) and possibly a ferric reductase (Cbyrd1). The role of Cbyrd1 is uncertain, as a knockout mouse has no defect in absorption (Gunshin et al. Blood, 2005, June 16, Epub). Transfer of iron to plasma is mediated by ferroportin (FPN). FPN's residence on the basolateral membrane is regulated by hepcidin (Nemeth et al. Science 2004, 306:2090–3). Iron absorption responds to erythropoiesis, hypoxia and iron stores. A dietary iron content of 120 mg/kg consumed will maintain hepatic iron stores near that of mice found in the wild. Mice will grow and breed given diets containing 35 mg/kg. Commercial mouse chow iron content ranges from 200–350 mg/kg. We studied the effects of diets containing 2, 35, 120, 350 and 2000 mg iron/kg on iron absorption, liver and spleen iron content and transcriptional levels of DMT1, FPN and hepcidin in A/J mice. Mice were weaned at 3 weeks of age and groups of 8 animals were placed on one of the 5 diets for 4 weeks. No differences between groups were noted in hematocrit, hemoglobin and MCV. Mean hepatic iron content was 52.7 ±3.7 ug/g (wet wt) in mice fed the 2 mg/kg diet. Mean hepatic iron content was 560 ±23.7 ug/g in mice fed the 2000 mg/kg diet. There was no difference in hepatic iron content in mice fed intermediate iron diets (35–350 mg/kg). Mean hepatic iron concentration in these groups was 110 ±3 ug/g. Mean spleen iron content was 132 ±12.2 ug/g (wet wt) in mice maintained on 2 mg/kg. Mean spleen iron content was 598 ±49 ug/g in mice fed the 2000 mg/kg diet. There was no difference in spleen iron content in mice maintained on intermediate iron diets (mean 359 ±10 ug/g). These data indicate that mice maintain constant levels of hepatic and splenic iron over a ten-fold range in dietary iron content. Iron absorption was measured as percent of a measured dose of 59Fe (5 ug total) remaining in the carcass (minus the GI tract) 24 h after administration by gavage. Absorption was inversely proportional to dietary iron content. Mean absorption was 86% ±4 in the group on the 2 mg/kg diet, 42% ±3 on the 35 mg/kg diet, 26% ±7 on the 120 mg/kg diet, 19% ±4 on the 350 mg/kg diet and 6% ±1 on the 2000 mg/kg diet. Transcript levels of hepcidin, DMT1 and FPN were measured by real-time PCR and normalized to beta actin mRNA. Liver hepcidin expression was 20-fold greater in mice on the 2000 mg/kg diet than in mice on the 2 mg/kg diet (3900 ±1021 copies/actin copy vs. 198 ±47). Hepcidin expression did not differ in mice on intermediate diets (745 ±147 copies). Enterocytes were isolated from everted gut explants by elution in EDTA. Transcript levels of enterocyte DMT1 and FPN were 4566 ±SEM and 236 ±SEM copies respectively in mice on the 2 mg/kg diet. No detectable transcripts were found in mice on the 2000 mg/kg diet. Enterocyte transcript levels for DMT1 and FPN were no different in groups on intermediate iron diets (17 ±2 copies and 20 ±9 copies respectively). These data indicate that tissue iron content, hepcidin, DMT1 and FPN remain constant over a ten-fold range in dietary iron and only vary at extremes, while iron absorption is inversely proportional to dietary iron. The data also suggest that dietary iron, within defined limits, regulates iron absorption by a mechanism intrinsic to the enterocyte.

Hepcidin Expression Is Correlated with Erythropoietic Indexes and Non-Transferrin-Bound Iron Levels in Patients with Thalassemia Major.

Hepcidin plays a central role in iron homeostasis. Hepcidin seems to be the common final mediator of both erythroid and stores regulators, and coordinates intestinal iron absorption and iron release from reticuloendothelial macrophages. The erythroid regulator probably dominates over the stores regulator. Iron overload in thalassemia major is attributed mainly to blood transfusions and partly to increased iron absorption. Urine hepcidin levels in regularly-transfused thalassemia patients are inappropriately low in regards to their iron stores. Liver hepcidin expression is suppressed in the murine model of human thalassemia (Hbbth3/+). We evaluated the correlation between indexes of iron stores and of erythropoiesis and liver hepcidin expression in patients with thalassemia major. Nineteen transfusion-dependent thalassemic patients (14 females) of 20±7.2 years of age underwent liver biopsy. Fourteen patients were seronegative for hepatitis C. Liver iron concentration (LIC) was estimated by atomic absorption spectrometry. Hepcidin mRNA expression levels were estimated by quantitative Real-Time PCR (Lightcycler, Roche) from isolated RNA from liver tissue. Hematologic and blood chemistry parameters were determined by standard methods. NTBI was measured in 13 patients by atomic absorption spectrometry. Statistical analysis was performed using non-parametric tests. Hepcidin expression ranged from 0.08 to 38.4 (median 1.13) arbitrary units. The most significant correlations between hepcidin and indexes of erythropoesis and of iron load are shown on the table.Variablemedian (range)hepcidinLICNTBIFerritin (μg/L)2174 (990–5963)n.s.n.s.n.s.Hb (g/dL)12 (11.2 – 13.4)r:0.55, P:.017r:-0.43, P:.071n.s.sTfR (mg/L)2.64 (0.75 – 5.75)r:-0.59, P:.01r:0.51, P:.03r:0.71, P:.006EPO (IU/L)21.6 (2.9 – 106)r:-0.61, P:.007r:0.56, P:.015r:0.63, P:.02NTBI (μmol/L)3.1 (0.9 – 4.5)r:0.56, P:.047r:0.67, P:.012LIC (μg Fe/d.w.tissue)8.3 (3.1 – 18.9)n.s.r = Spearman's rho, n.s. = non statisticalThe correlations between hepcidin and Hb, sTfR, EPO were stronger when patients with infectious hepatitis were excluded from analysis. Hepcidin did not correlate with any indexes of iron load, including LIC, ferritin, serum iron, transferrin saturation and annual transfusional iron load. Our results provide additional evidence that increased erythropoietic activity down-regulates hepcidin expression. The lack of correlation between iron stores and hepcidin expression is in consistency with the hypothesis that increased erythropoietic activity dominates over iron stores in the regulation of hepcidin expression in patients with thalassemia major. Furthermore, the negative correlation between NTBI and hepcidin RNA levels underlies the role of hepcidin in iron body trafficking even in hemosiderotic patients.

Role of interleukin‐6 in hypoxic regulation of intestinal iron absorption

The regulation of intestinal iron absorption is not fully understood. Hepcidin, a liver-produced peptide, has recently been identified as a negative regulator of iron absorption in various conditions associated with altered iron metabolism (e.g. inflammation, anaemia, hypoxia). It is not clear whether these perturbants share a common signalling pathway. In this study, the importance of the cytokine interleukin-6 (IL-6) was investigated in the hypoxic mouse model. Hypoxia was associated with increased levels of circulating IL-6, decreased liver hepcidin mRNA and increased iron absorption (especially MT). A significant positive correlation existed between the total iron uptake and IL-6 levels in circulation. IL-6 per se, though inducing hepcidin mRNA, failed to affect basal iron absorption. The adaptive response to absorption following the hypoxic exposure was, however, more prominent if mice had been treated concurrently with IL-6. This enhancement in absorption occurred even though hepcidin mRNA was not significantly changed. Similar prominent responses were seen with both human and mouse IL-6. Anti-IL-6 antiserum normalised iron absorption in mice exposed to hypoxia, because of a reduction in the MT. These data indicate that IL-6 can influence iron absorption (especially MT) during the hypoxic exposure, but via a mechanism independent of hepcidin.

Contribution of Hfe expression in macrophages to the regulation of hepatic hepcidin levels and iron loading

AbstractHereditary hemochromatosis (HH), an iron overload disease associated with mutations in the HFE gene, is characterized by increased intestinal iron absorption and consequent deposition of excess iron, primarily in the liver. Patients with HH and Hfe-deficient (Hfe-/-) mice manifest inappropriate expression of the iron absorption regulator hepcidin, a peptide hormone produced by the liver in response to iron loading. In this study, we investigated the contribution of Hfe expression in macrophages to the regulation of liver hepcidin levels and iron loading. We used bone marrow transplantation to generate wild-type (wt) and Hfe-/- mice chimeric for macrophage Hfe gene expression. Reconstitution of Hfe-deficient mice with wt bone marrow resulted in augmented capacity of the spleen to store iron and in significantly decreased liver iron loading, accompanied by a significant increase of hepatic hepcidin mRNA levels. Conversely, wt mice reconstituted with Hfe-deficient bone marrow had a diminished capacity to store iron in the spleen but no significant alterations of liver iron stores or hepcidin mRNA levels. Our results suggest that macrophage Hfe participates in the regulation of splenic and liver iron concentrations and liver hepcidin expression. (Blood. 2005;106:2189-2195)

Hepcidin levels in humans are correlated with hepatic iron stores, hemoglobin levels, and hepatic function

AbstractHepcidin, a key regulator of iron metabolism, is synthesized by the liver. Hepcidin binds to the iron exporter ferroportin to regulate the release of iron into plasma from macrophages, hepatocytes, and enterocytes. We analyzed liver samples from patients undergoing hepatic surgery for cancer or receiving liver transplants and analyzed correlations between clinical parameters and liver hepcidin mRNA and urinary hepcidin concentrations. Despite the many potential confounding influences, urinary hepcidin concentrations significantly correlated with hepatic hepcidin mRNA concentrations, indicating that hepcidin quantification in urine is a valid approach to evaluate hepcidin expression. Moreover, we found in humans that hepcidin levels correlated with hepatic iron stores and hemoglobin levels and may also be affected by hepatic dysfunction. (Blood. 2005;106:746-748)

Ischemia‐reperfusion of rat liver modulates hepcidin in vivo expression

The recently identified acute-phase response antimicrobial peptide hepcidin has been postulated to maintain iron homeostasis by modulating iron absorption at both the intestinal and macrophage levels. Hepcidin has also been reported to be responsible for anemia associated with chronic inflammatory diseases, and in anemia in patients with hepatic adenomas. Since Kupffer cells are known to be the primary contributor to early-phase ischemia-reperfusion injury in the liver and iron is known to modulate Kupffer cell production of proinflammatory cytokine and reactive oxygen species, we investigated hepcidin in vivo expression in the well-established rat partial-liver ischemia-reperfusion model. We found that both liver ischemia alone and liver ischemia-reperfusion significantly induced serum and liver hepcidin levels. Furthermore, currently proposed mediators of in vivo hepcidin expression, such as interleukin-6, signal transducers and activators of transcription-family transducers, and CCAAT/enhancing binding protein-alpha do not appear to modulate hepcidin expression in the liver ischemia-reperfusion acute inflammatory model. In this study we report the first in vivo evidence of liver ischemia and liver ischemia-reperfusion modulation of hepcidin expression. In conclusion, in the well-characterized liver ischemia-reperfusion model of acute inflammation, mechanism(s) other than interleukin-6 signal transduction via signal transducers and activators of transcription-3 may be responsible for hepcidin induction.

Iron‐ and inflammation‐induced hepcidin gene expression in mice is not mediated by Kupffer cells in vivo†

Hepcidin, a recently discovered iron regulatory peptide, is believed to inhibit the release of iron from absorptive enterocytes and macrophages. Liver hepcidin synthesis is induced in vivo by iron stores and inflammation. The molecular basis of the regulation of hepcidin gene expression by these effectors in hepatocytes is currently unknown, although there is strong evidence that indirect mechanisms are involved. The aims of this study were to gain insight into these mechanisms and to determine to what extent other liver cell types are responsible for transducing the signal by which hepcidin expression is regulated in mouse hepatocytes. For this, we depleted Kupffer cells by injection of liposome-encapsulated clodronate and then studied iron- and inflammation-induced hepcidin gene expression. In addition, we directly evaluated the role of the inflammatory cytokine interleukin 6 (IL-6) by using IL-6-deficient mice. Our results show that iron is able to induce hepcidin gene expression independently of Kupffer cells in the liver and circulating IL-6. In contrast, we show that hepcidin gene induction by inflammation is also independent of Kupffer cells, but involves, at least partly, IL-6. In conclusion, these results show that two independent regulatory pathways control hepcidin gene expression and suggest that hepatocytes play a key role in the regulation of hepcidin gene expression by sensing iron and inflammatory signals.

Hepcidin Expression in Cultured Liver Cells Responds Differently to Iron Overloaded Sera Derived from Patients with Thalassemia and Hemochromatosis.

We have recently shown that hepcidin expression undergoes a significant down regulation in the liver of a thalassaemia intermedia mouse model (TIM) C57Bl/6 Hbbth3/+. (Adamsky K. et al. BJH 2004; 124(1):123–4). We extended these studies to a b-thalassemia major mouse model (TMM) generated via engraftment with beta-globin-null (Hbbth3/th3) fetal liver cells. The resulting phenotype displayed considerably more severe symptoms than the TIM: the TMM succumbed to ineffective erythropoiesis within 60 days, developed massive splenomegaly, severe anemia, extramedullary hematopoiesis and hepatic iron overload. The expression levels of various iron metabolism-related genes (normalized to b-actin) were analyzed by quantitative RT-PCR on RNA extracted from the livers of adult mice. When compared to wild-type (WT) C57Bl/6 mice, the liver mRNA expression levels of TMM were markedly reduced for hepcidin and TfR2 (16 and 3 fold respectively), markedly increased for the lipocalin NGAL and transferrin receptor 1 (TfR1) (2.7 and 3.6 fold respectively), moderately increased for the ferroportin transporter (IREG1) (1.4 fold) and unaltered for the hemochromatosis gene (HFE). A possible mechanism that could explain the decreased expression of liver hepcidin in thalassaemia is one based on a putative regulatory serum factor that is associated with enhanced erythropoietic activity. In order to assess this hypothesis we compared the hepcidin inductive capacity of sera from iron-overloaded patients that either had or had not enhanced erythropoiesis, namely thalassemia and hemochromatosis, respectively. These included the following individuals: 14 with β-thalassemia major, 22 with hereditary hemochromatosis (HFE 282C mutation) and 3 healthy. The human sera were analyzed in terms of their capacity to modulate expression of iron-related genes in human hepatoma HepG2 cells, using quantitative RT-PCR. Hepcidin expression evoked by thalassemic sera was an average of 3 fold lower than that evoked by normal human serum, whereas hemochromatotic sera evoked an average of 7.83 fold increase. The down regulating effect of thalassemic sera on hepcidin expression, suggests the possible involvement of an upstream factor whose serum levels might increase in thalassemia due to ineffective erythropoiesis, i.e. an “erythropoietic regulator”. The effect of such an “erythropoietic regulator” is assumed to override the expected increase in hepcidin expression that results from the “stores regulator” which is responsive to iron overload such as in hemochromatosis (where there is no ineffective erythropoiesis). The reduced hepcidin expression found in thalassaemia might explain the increased enteric iron absorption whose extent could be moderated either by factors that increase hepcidin expression or by administration of hepcidin itself.

Decreased Serum Pro-Hepcidin in Thalassaemia Intermedia; a Mechanism for Increased Iron Absortion Mediated Though Ineffective Erthropoiesis and NTBI?.

Background: Pro-hepcidin is 10 kDa peptide localized at the basolateral membrane of hepatocytes which is also present in plasma and is believed to be a hepcidin precursor (Kulaksis et al, Gut 2004;53). Experimental hepatic iron loading in mice up-regulates hepcidin mRNA while iron deficiency has the reverse effect (Pigeon et al, JBC 2001;276). Paradoxically mice with a thalassaemia intermedia phenotype had reduced liver hepcidin mRNA. Furthermore, presentation of non-transferrin bound iron (NTBI) to human liver cells (Nemeth, Blood 2003; 101)(Rafique, 2004 in preparation) decreased hepcidin mRNA. Patients and methods: 3 groups of patients were compared (thalassaemia major (TM), thalassaemia intermedia (TI) and sickle cell anaemia (HbSS)) to examine if variations in pro-hepcidin expression could account for the differences in iron loading. Pro-hepcidin measurements were performed at 1:1 dilutions in duplicate with a Pro-hepcidin ELISA (DRG diagnostics) using a previously published method (Kulakis, 2004). Iron status was evaluted by liver CMR , serum ferritin and NTBI; C reactive protein (CRP) was measured to exclude inflammation. All patients with a raised creatinine were excluded from the analysis. Results: TI patients (n=20) had a significantly lower serum pro-hepcidin (77 ± 40ng/ml) ( p<0.001) compared to HbSS (n=26) (111 ± 53 ng/ml), TM (n=27) (107 ± 44.5ng/ml) or control subjects (n=9) (119 ± 45ng/ml). The difference in serum pro-hepicidin between TI and HbSS persisted when patients were matched for serum ferritin (p = 0.02) or liver iron (p < 0.001). NTBI was significantly lower in HbSS (1.06 ± 0.27umol/l) than TI (2.49 ± 2.01 umol/l) even when patients were matched for serum ferritin (p <0.001) or for liver iron (p <0.05). Hb values were not significantly different between TI (8.6 g/dl) and HbSS patients (8.9g/dl). When all patients with a Hb <8g/dl were compared to those with a Hb > 10g/dl serum pro-hepcidin was not significantly different. No correlation between serum pro-hepcidin and liver iron, serum ferritin, CRP or Hb in any of the three groups was seen. Conclusion: Pro-hepcidin is significantly lower in TI than TM or HbSS patients and this cannot be accounted for by levels of anemia. We propose that NTBI, present early in TI secondary to high ineffective erythropoiesis, may lead to a similar paradoxical decrease in hepcidin synthesis reported in model systems and that this is reflected by reduced serum pro-hepcidin. Although levels of NTBI and liver iron did not differ significantly in TI and TM , transfusion and chelation therapy in TM may overide the NTBI mediated down regulation of pro-hepcidin. In HbSS, NTBI is lower than in TI or TM at matched levels of iron loading, resulting in less inhibition of pro-hepcidin synthesis and less duodenal iron absorption than in TI.

Effect of altered iron metabolism on markers of haem biosynthesis and intestinal iron absorption in mice.

In this study, well-characterised animal models of altered iron metabolism were used to investigate link(s) between haem biosynthesis and intestinal iron absorption. Mice rendered iron deficient by feeding a low-iron diet for 3-4 weeks showed low levels of hepatic non-haem iron and hepcidin mRNA, with reduced urinary 5-aminolaevulinic acid (ALA) excretion and enhanced intestinal iron absorption. Hepatic ALA synthase activity was reduced while ALA dehydratase activity was increased. Iron-loaded mice had markedly increased liver non-haem iron and hepcidin mRNA, with increased urinary ALA excretion. Intestinal iron absorption was decreased mainly due to a reduction in transfer of absorbed iron from mucosa to the carcass. Hepatic ALA synthase activity was increased and ALA dehydratase activity moderately reduced. Mice exposed to hypoxia (0.5 atm) for 1-3 days had reduced hepatic hepcidin mRNA and urinary ALA excretion, while intestinal iron absorption was increased. Hepatic ALA synthase activity was reduced. The ALA dehydratase activity in liver and spleen was markedly enhanced. Injection of ALA to iron-deficient mice or hypoxic mice reduced their intestinal iron absorption to normal levels. This study further supports the hypothesis that alterations in haem biosynthesis influence duodenal iron absorption. ALA in particular appears to function as a modulator in controlling intestinal iron absorption.

Effect of hepcidin on intestinal iron absorption in mice

AbstractThe effect of the putative iron regulatory peptide hepcidin on iron absorption was investigated in mice. Hepcidin peptide was synthesized and injected into mice for up to 3 days, and in vivo iron absorption was measured with tied-off segments of duodenum. Liver hepcidin expression was measured by reverse transcriptase–polymerase chain reaction. Hepcidin significantly reduced mucosal iron uptake and transfer to the carcass at doses of at least 10 μg/mouse per day, the reduction in transfer to the carcass being proportional to the reduction in iron uptake. Synthetic hepcidin injections down-regulated endogenous liver hepcidin expression excluding the possibility that synthetic hepcidin was functioning by a secondary induction of endogenous hepcidin. The effect of hepcidin was significant at least 24 hours after injection of hepcidin. Liver iron stores and hemoglobin levels were unaffected by hepcidin injection. Similar effects of hepcidin on iron absorption were seen in iron-deficient and Hfe knockout mice. Hepcidin inhibited the uptake step of duodenal iron absorption but did not affect the proportion of iron transferred to the circulation. The effect was independent of iron status of mice and did not require Hfe gene product. The data support a key role for hepcidin in the regulation of intestinal iron uptake.

Decreased Liver Hepcidin Expression in the Hfe Knockout Mouse

ABSTRACT Hepcidin is a circulating antimicrobial peptide which has been proposed to regulate the uptake of dietary iron and its storage in reticuloendothelial macrophages. Transgenic mice lacking hepcidin expression demonstrate abnormalities of iron homeostasis similar to Hfe knockout mice and to patients with HFE-associated hereditary hemochromatosis (HH). To identify any association between liver hepcidin expression and the iron homeostasis abnormalities observed in HH, we compared liver hepcidin mRNA content in wild type and Hfe knockout mice. Because the iron homeostasis abnormalities in the Hfe knockout mice are greatest early in life, we analyzed mice at different ages. At four weeks of age, Hfe knockout mice had significantly decreased liver hepcidin mRNA expression compared to wild type mice. The decreased hepcidin expression was associated with hepatic iron deposition, elevated transferrin saturations, and decreased splenic iron concentrations. At 10 weeks of age, despite marked hepatic iron loading, Hfe knockout mice demonstrated liver hepcidin mRNA expression similar to that observed in wild type mice. Placing 8 week-old wild type and Hfe knockout mice on a 2% carbonyl iron diet for 2 weeks led to a similar degree of hepatic iron loading in each group. However, while the wild type mice demonstrated a mean five-fold increase in liver hepcidin mRNA, no change was observed in the Hfe knockout mice. The lack of an increase in liver hepcidin expression in these iron-loaded Hfe knockout mice was associated with sparing of iron deposition into the spleen. These data indicate that the normal relationship between body iron stores and liver hepcidin mRNA levels is altered in Hfe knockout mice, such that liver hepcidin expression is relatively decreased. We speculate that decreased hepcidin expression relative to body iron stores contributes to the iron homeostasis abnormalities characteristic of HH.

The gene encoding the iron regulatory peptide hepcidin is regulated by anemia, hypoxia, and inflammation.

The present study was aimed at determining whether hepcidin, a recently identified peptide involved in iron metabolism, plays a role in conditions associated with both iron overload and iron deficiency. Hepcidin mRNA levels were assessed in two models of anemia, acute hemolysis provoked by phenylhydrazine and bleeding provoked by repeated phlebotomies. Hepcidin response to hypoxia was also studied, both ex vivo, in human hepatoma cells, and in vivo. Anemia and hypoxia were associated with a dramatic decrease in liver hepcidin gene expression, which may account for the increase in iron release from reticuloendothelial cells and increase in iron absorption frequently observed in these situations. A single injection of turpentine for 16 hours induced a sixfold increase in liver hepcidin mRNA levels and a twofold decrease in serum iron. The hyposideremic effect of turpentine was completely blunted in hepcidin-deficient mice, revealing hepcidin participation in anemia of inflammatory states. These modifications of hepcidin gene expression further suggest a key role for hepcidin in iron homeostasis under various pathophysiological conditions, which may support the pharmaceutical use of hepcidin agonists and antagonists in various iron homeostasis disorders.

The gene encoding the iron regulatory peptide hepcidin is regulated by anemia, hypoxia, and inflammation

The present study was aimed at determining whether hepcidin, a recently identified peptide involved in iron metabolism, plays a role in conditions associated with both iron overload and iron deficiency. Hepcidin mRNA levels were assessed in two models of anemia, acute hemolysis provoked by phenylhydrazine and bleeding provoked by repeated phlebotomies. Hepcidin response to hypoxia was also studied, both ex vivo, in human hepatoma cells, and in vivo. Anemia and hypoxia were associated with a dramatic decrease in liver hepcidin gene expression, which may account for the increase in iron release from reticuloendothelial cells and increase in iron absorption frequently observed in these situations. A single injection of turpentine for 16 hours induced a sixfold increase in liver hepcidin mRNA levels and a twofold decrease in serum iron. The hyposideremic effect of turpentine was completely blunted in hepcidin-deficient mice, revealing hepcidin participation in anemia of inflammatory states. These modifications of hepcidin gene expression further suggest a key role for hepcidin in iron homeostasis under various pathophysiological conditions, which may support the pharmaceutical use of hepcidin agonists and antagonists in various iron homeostasis disorders.