Inhibition of hepcidin transcription by growth factors

Deciphering the role of hepcidin in iron metabolism and anemia management

One of the most common diseases worldwide is anemia, which is characterized by insufficient erythrocyte production. Numerous complex factors, such as chronic diseases, genetic mutations, and nutritional inadequacies, contribute to this widespread syndrome. This review focuses specifically on anemias caused by defective hepcidin production. Hepcidin, a peptide hormone produced primarily by liver cells, plays a crucial role in regulating iron levels by controlling its absorption. Hepcidin's mechanism of action involves binding to the ferroportin iron transporter, causing its internalization. Disturbances in iron metabolism can have far-reaching consequences, affecting not only the blood but also organs like the liver, kidneys, and brain. Iron homeostasis is crucial for maintaining optimal physiological function. Several blood-based markers are employed to assess iron stores. However, these markers have inherent limitations. Hepcidin, a key regulator of iron metabolism, plays a pivotal role in preventing iron release into the plasma from absorptive enterocytes and macrophages. Elucidating the structure and function of hepcidin is essential for understanding its role in iron homeostasis, which has significant implications for the diagnosis and management of various anemia subtypes. A well-established correlation exists between hepcidin dysregulation and iron deficiency. Despite its potential as a biomarker, the clinical application of hepcidin is hindered by the lack of a commercially available, clinically validated assay. This review aims to provide a comprehensive overview of hepcidin's role in regulating blood iron concentrations and elucidate its implications in the pathogenesis of various anemia subtypes, paving the way for its future applications in research and clinical practice.

The effect of iron supplementation in preterm infants at different gestational ages

BACKGROUND

Iron deficiency (ID) is the most prevalent nutritional deficiency disease in preterm infants, significantly affecting their growth and development. For preterm infants to flourish physically and neurologically, timely iron supplementation is essential. The main goals of this study were to determine whether the present iron supplementation regimen results in iron overload in late preterm infants and whether it can meet the growth requirements of early preterm infants for catch-up.

METHODS

We conducted a prospective follow-up study on preterm infants at the Department of Child Health, West China Second University Hospital, Sichuan University, from January 1, 2020, to August 31, 2020. In this study, 177 preterm infants were divided into two groups based on gestational age-early preterm infants (gestational age < 34 weeks) and late preterm infants (gestational age ≥ 34 weeks and < 37 weeks)-to compare the incidence of iron deficiency, iron status, and physical growth of preterm infants receiving iron supplements (2-4 mg/kg/d).

RESULTS

Iron supplementation considerably reduced the incidence of iron deficiency in preterm infants. The prevalence of iron deficiency in early preterm infants and late preterm infants was 11.3% and 5.1%, respectively, at the corrected gestational age of 3 months; at the corrected gestational age of 6 months, the prevalence was 5.3% and 6.3%, respectively. No preterm infants with iron deficiency were detected in either group at the corrected gestational age of 12 months. Ferritin was substantially lower in early preterm infants (36.87 ± 31.57 ng/ml) than in late preterm infants (65.78 ± 75.76 ng/ml) at the corrected gestational age of 3 months (p < 0.05). A multifactorial regression analysis of factors influencing iron metabolism levels in preterm infants revealed a positive relationship between log10hepcidin, birth weight, and ferritin, with higher birth weights resulting in higher ferritin levels.

CONCLUSIONS

Postnatal iron supplementation at 2-4 mg/kg/d in preterm infants significantly decreases the incidence of ID. There were substantial differences in iron levels across preterm infants of varying gestational ages. A tailored iron supplementation plan based on growth, birth weight, and gestational age may be a more suitable route for iron supplementation. Although the current study found that the postnatal iron status of early preterm infants differed from that of late preterm infants, the actual mechanism of action remains unknown, and large-sample, multicenter clinical studies are required to investigate this further.

Reactive oxygen species regulation by NCF1 governs ferroptosis susceptibility of Kupffer cells to MASH

Impaired self-renewal of Kupffer cells (KCs) leads to inflammation in metabolic dysfunction-associated steatohepatitis (MASH). Here, we identify neutrophil cytosolic factor 1 (NCF1) as a critical regulator of iron homeostasis in KCs. NCF1 is upregulated in liver macrophages and dendritic cells in humans with metabolic dysfunction-associated steatotic liver disease and in MASH mice. Macrophage NCF1, but not dendritic cell NCF1, triggers KC iron overload, ferroptosis, and monocyte-derived macrophage infiltration, thus aggravating MASH progression. Mechanistically, elevated oxidized phospholipids induced by macrophage NCF1 promote Toll-like receptor (TLR4)-dependent hepatocyte hepcidin production, leading to increased KC iron deposition and subsequent KC ferroptosis. Importantly, the human low-functional polymorphic variant NCF190H alleviates KC ferroptosis and MASH in mice. In conclusion, macrophage NCF1 impairs iron homeostasis in KCs by oxidizing phospholipids, triggering hepatocyte hepcidin release and KC ferroptosis in MASH, highlighting NCF1 as a therapeutic target for improving KC fate and limiting MASH progression.

Active Components of Pueraria lobata through the MAPK/ERK Signaling Pathway Alleviate Iron Overload in Alcoholic Liver Disease

OBJECTIVE

To delve into the primary active ingredients and mechanism of Pueraria lobata for alleviating iron overload in alcoholic liver disease.

METHODS

Pueraria lobata's potential targets and signaling pathways in treating alcohol-induced iron overloads were predicted using network pharmacology analysis. Then, animal experiments were used to validate the predictions of network pharmacology. The impact of puerarin or genistein on alcohol-induced iron accumulation, liver injury, oxidative stress, and apoptosis was assessed using morphological examination, biochemical index test, and immunofluorescence. Key proteins implicated in linked pathways were identified using RT-qPCR, western blot analysis, and immunohistochemistry.

RESULTS

Network pharmacological predictions combined with animal experiments suggest that the model group compared to the control group, exhibited activation of the MAPK/ERK signaling pathway, suppression of hepcidin expression, and aggravated iron overload, liver damage, oxidative stress, and hepatocyte death. Puerarin and genistein, the active compounds in Pueraria lobata, effectively mitigated the aforementioned alcohol-induced effects. No statistically significant disparities were seen in the effects above between the two groups receiving drug therapy.

CONCLUSION

This study preliminarily demonstrated that puerarin and genistein in Pueraria lobata may increase hepcidin production to alleviate alcohol-induced iron overload by inhibiting the MAPK/ERK signaling pathway.

Human umbilical cord mesenchymal stem cells protect against ferroptosis in acute liver failure through the IGF1-hepcidin-FPN1 axis and inhibiting iron loading

Acute liver failure (ALF) is a significant global issue with elevated morbidity and mortality rates. There is an urgent and pressing need for secure and effective treatments. Ferroptosis, a novel iron-dependent regulation of cell death, plays a significant role in multiple pathological processes associated with liver diseases, including ALF. Several studies have demonstrated that mesenchymal stem cells (MSCs) have promising therapeutic potential in the treatment of ALF. This study aims to investigate the positive effects of MSCs against ferroptosis in an ALF model and explore the underlying molecular mechanisms of their therapeutic function. Our results show that intravenously injected MSCs protect against ferroptosis in ALF mouse models. MSCs decrease iron deposition in the liver of ALF mice by downregulating hepcidin level and upregulating FPN1 level. MSCs labelled with Dil are mainly observed in the hepatic sinusoid and exhibit colocalization with the macrophage marker CD11b fluorescence. ELISA demonstrates a high level of IGF1 in the CCL 4+MSC group. Suppressing the IGF1 effect by the PPP blocks the therapeutic effect of MSCs against ferroptosis in ALF mice. Furthermore, disruption of IGF1 function results in iron deposition in the liver tissue due to impaired inhibitory effects of MSCs on hepcidin level. Our findings suggest that MSCs alleviate ferroptosis induced by disorders of iron metabolism in ALF mice by elevating IGF1 level. Moreover, MSCs are identified as a promising cell source for ferroptosis treatment in ALF mice.

Protective Effects and Mechanism of Polysaccharides from Edible Medicinal Plants in Alcoholic Liver Injury: A Review

Alcohol use accounts for a large variety of diseases, among which alcoholic liver injury (ALI) poses a serious threat to human health. In order to overcome the limitations of chemotherapeutic agents, some natural constituents, especially polysaccharides from edible medicinal plants (PEMPs), have been applied for the prevention and treatment of ALI. In this review, the protective effects of PEMPs on acute, subacute, subchronic, and chronic ALI are summarized. The pathogenesis of alcoholic liver injury is analyzed. The structure-activity relationship (SAR) and safety of PEMPs are discussed. In addition, the mechanism underlying the hepatoprotective activity of polysaccharides from edible medicinal plants is explored. PEMPs with hepatoprotective activities mainly belong to the families Orchidaceae, Solanaceae, and Liliaceae. The possible mechanisms of PEMPs include activating enzymes related to alcohol metabolism, attenuating damage from oxidative stress, regulating cytokines, inhibiting the apoptosis of hepatocytes, improving mitochondrial function, and regulating the gut microbiota. Strategies for further research into the practical application of PEMPs for ALI are proposed. Future studies on the mechanism of action of PEMPs will need to focus more on the utilization of multi-omics approaches, such as proteomics, epigenomics, and lipidomics.

Iron homeostasis in full-term, normal birthweight Gambian neonates over the first week of life

Human neonates elicit a profound hypoferremia which may protect against bacterial sepsis. We examined the transience of this hypoferremia by measuring iron and its chaperone proteins, inflammatory and haematological parameters over the first post-partum week. We prospectively studied term, normal weight Gambian newborns. Umbilical cord vein and artery, and serial venous blood samples up to day 7 were collected. Hepcidin, serum iron, transferrin, transferrin saturation, haptoglobin, c-reactive protein, α1-acid-glycoprotein, soluble transferrin receptor, ferritin, unbound iron-binding capacity and full blood count were assayed. In 278 neonates we confirmed the profound early postnatal decrease in serum iron (22.7 ± 7.0 µmol/L at birth to 7.3 ± 4.6 µmol/L during the first 6-24 h after birth) and transferrin saturation (50.2 ± 16.7% to 14.4 ± 6.1%). Both variables increased steadily to reach 16.5 ± 3.9 µmol/L and 36.6 ± 9.2% at day 7. Hepcidin increased rapidly during the first 24 h of life (19.4 ± 14.4 ng/ml to 38.9 ± 23.9 ng/ml) and then dipped (32.7 ± 18.4 ng/ml) before rising again at one week after birth (45.2 ± 19.1 ng/ml). Inflammatory markers increased during the first week of life. The acute postnatal hypoferremia in human neonates on the first day of life is highly reproducible but transient. The rise in serum iron during the first week of life occurs despite very high hepcidin levels indicating partial hepcidin resistance.Trial Registration: clinicaltrials.gov (NCT03353051). Registration date: November 27, 2017.

Dynamic chromatin accessibility during nutritional iron overload reveals a BMP6-independent induction of cell cycle genes

Iron is essential to organism physiology as it participates in numerous biological processes including oxygen transport, respiration and erythropoiesis. Although iron is critical to physiology, excess iron is toxic to cells and tissues due to generation of reactive oxygen species. Therefore, well-kept iron homeostasis is a mainstay of proper cell and organ function. Iron overload disorders, caused by nutritional or genetic factors, contribute to many pathologies such as diabetes, non-alcoholic steatohepatitis and hepatocellular carcinoma. The liver is not only vulnerable to the effects of iron overload, it is also the major organ controlling iron homeostasis. During iron overload, Bone Morphogenic Protein (BMP) levels increase and initiate a hepatic response aimed at lowering iron levels. The transcriptional effects of iron overload are not well-characterized and the underlining enhancer regulation is uncharted. Here, we profiled the liver's transcriptome and chromatin accessibility following nutritional iron overload. We found marked changes in gene expression and enhancer accessibility following iron overload. Surprisingly, 16% of genes induced following iron overload participate in propagating the cell cycle. Induction of cell cycle genes was independent of BMP. Genome-wide enhancer landscape profiling revealed hundreds of enhancers with altered activity following iron overload. Characterization of transcription factor motifs and footprints in iron-regulated enhancers showed a role for the Activator Protein 1 (AP-1) transcription factor in promoting cell cycle-related transcription. In summary, we found that the transcriptional program at play during iron overload is bifurcated in which BMP signaling controls iron homeostasis genes while an AP-1-driven program controls cell cycle genes.

The hepatokine FGL1 regulates hepcidin and iron metabolism during the recovery from hemorrhage-induced anemia in mice

As a functional component of erythrocyte hemoglobin, iron is essential for oxygen delivery to all tissues in the body. The liver-derived peptide hepcidin is the master regulator of iron homeostasis. During anemia, the erythroid hormone erythroferrone regulates hepcidin synthesis to ensure adequate supply of iron to the bone marrow for red blood cells production. However, mounting evidence suggested that another factor may exert a similar function. We identified the hepatokine FGL1 as a previously undescribed suppressor of hepcidin that is induced in the liver in response to hypoxia during the recovery from anemia and in thalassemic mice. We demonstrated that FGL1 is a potent suppressor of hepcidin in vitro and in vivo . Deletion of Fgl1 in mice results in a blunted repression of hepcidin after bleeding. FGL1 exerts its activity by direct binding to BMP6, thereby inhibiting the canonical BMP-SMAD signaling cascade that controls hepcidin transcription.

Key points

1/ FGL1 regulates iron metabolism during the recovery from anemia. 2/ FGL1 is an antagonist of the BMP/SMAD signaling pathway.

Distinctive modulation of hepcidin in cancer and its therapeutic relevance

Hepcidin, a short peptide synthesized primarily by hepatocytes in response to increased body iron and inflammation, is a crucial iron-regulating factor. Hepcidin regulates intestinal iron absorption and releases iron from macrophages into plasma through a negative iron feedback mechanism. The discovery of hepcidin inspired a torrent of research into iron metabolism and related problems, which have radically altered our understanding of human diseases caused by an excess of iron, an iron deficiency, or an iron disparity. It is critical to decipher how tumor cells manage hepcidin expression for their metabolic requirements because iron is necessary for cell survival, particularly for highly active cells like tumor cells. Studies show that tumor and non-tumor cells express and control hepcidin differently. These variations should be explored to produce potential novel cancer treatments. The ability to regulate hepcidin expression to deprive cancer cells of iron may be a new weapon against cancer cells.

A contemporary understanding of iron metabolism in active premenopausal females

Iron metabolism research in the past decade has identified menstrual blood loss as a key contributor to the prevalence of iron deficiency in premenopausal females. The reproductive hormones estrogen and progesterone influence iron regulation and contribute to variations in iron parameters throughout the menstrual cycle. Despite the high prevalence of iron deficiency in premenopausal females, scant research has investigated female-specific causes and treatments for iron deficiency. In this review, we provide a comprehensive discussion of factors that influence iron status in active premenopausal females, with a focus on the menstrual cycle. We also outline several practical guidelines for monitoring, diagnosing, and treating iron deficiency in premenopausal females. Finally, we highlight several areas for further research to enhance the understanding of iron metabolism in this at-risk population.

Iron overload in alcoholic liver disease: underlying mechanisms, detrimental effects, and potential therapeutic targets

Alcoholic liver disease (ALD) is a global public health challenge due to the high incidence and lack of effective therapeutics. Evidence from animal studies and ALD patients has demonstrated that iron overload is a hallmark of ALD. Ethanol exposure can promote iron absorption by downregulating the hepcidin expression, which is probably mediated by inducing oxidative stress and promoting erythropoietin (EPO) production. In addition, ethanol may enhance iron uptake in hepatocytes by upregulating the expression of transferrin receptor (TfR). Iron overload in the liver can aggravate ethanol-elicited liver damage by potentiating oxidative stress via Fenton reaction, promoting activation of Kupffer cells (KCs) and hepatic stellate cells (HSCs), and inducing a recently discovered programmed iron-dependent cell death, ferroptosis. This article reviews the current knowledge of iron metabolism, regulators of iron homeostasis, the mechanism of ethanol-induced iron overload, detrimental effects of iron overload in the liver, and potential therapeutic targets.

Coordination of iron homeostasis by bone morphogenetic proteins: Current understanding and unanswered questions

Iron homeostasis is tightly regulated to balance the iron requirement for erythropoiesis and other vital cellular functions, while preventing cellular injury from iron excess. The liver hormone hepcidin is the master regulator of systemic iron balance by controlling the degradation and function of the sole known mammalian iron exporter ferroportin. Liver hepcidin expression is coordinately regulated by several signals that indicate the need for more or less iron, including plasma and tissue iron levels, inflammation, and erythropoietic drive. Most of these signals regulate hepcidin expression by modulating the activity of the bone morphogenetic protein (BMP)-SMAD pathway, which controls hepcidin transcription. Genetic disorders of iron overload and iron deficiency have identified several hepatocyte membrane proteins that play a critical role in mediating the BMP-SMAD and hepcidin regulatory response to iron. However, the precise molecular mechanisms by which serum and tissue iron levels are sensed to regulate BMP ligand production and promote the physical and/or functional interaction of these proteins to modulate SMAD signaling and hepcidin expression remain uncertain. This critical commentary will focus on the current understanding and key unanswered questions regarding how the liver senses iron levels to regulate BMP-SMAD signaling and thereby hepcidin expression to control systemic iron homeostasis.

20 years of Hepcidin: How far we have come

Twenty years ago the discovery of hepcidin deeply changed our understanding of the regulation of systemic iron homeostasis. It is now clear that hepcidin orchestrates systemic iron levels by controlling the amount of iron exported into the bloodstream through ferroportin. Hepcidin expression is increased in situations where systemic iron levels should be reduced, such as in iron overload and infection. Conversely, hepcidin is repressed during iron deficiency, hypoxia or expanded erythropoiesis, to increase systemic iron availability and sustain erythropoiesis. In this review, we will focus on molecular mechanisms of hepcidin regulation and on the pathological consequences of their disruption.

Physiological and pathophysiological mechanisms of hepcidin regulation: clinical implications for iron disorders

The discovery of hepcidin has provided a solid foundation for understanding the mechanisms of systemic iron homeostasis and the aetiologies of iron disorders. Hepcidin assures the balance of circulating and stored iron levels for multiple physiological processes including oxygen transport and erythropoiesis, while limiting the toxicity of excess iron. The liver is the major site where regulatory signals from iron, erythropoietic drive and inflammation are integrated to control hepcidin production. Pathologically, hepcidin dysregulation by genetic inactivation, ineffective erythropoiesis, or inflammation leads to diseases of iron deficiency or overload such as iron-refractory iron-deficiency anaemia, anaemia of inflammation, iron-loading anaemias and hereditary haemochromatosis. In the present review, we discuss recent insights into the molecular mechanisms governing hepcidin regulation, how these pathways are disrupted in iron disorders, and how this knowledge is being used to develop novel diagnostic and therapeutic strategies.

Hepcidin Signaling in Health and Disease: Ironing Out the Details

Hepcidin, a peptide hormone produced by hepatocytes, is the central regulator of systemic iron homeostasis through its interaction with ferroportin, the major cellular iron export protein. Hepcidin binding to ferroportin results in reduced iron export from macrophages and intestinal absorptive cells, leading to decreased serum iron levels. Hepcidin expression is influenced by several factors that include serum and liver iron stores, erythropoiesis, hypoxia, inflammation, and infection. Erythropoietic drive and hypoxia suppress hepcidin expression and promote red cell production. In contrast, inflammation and infection are associated with increased hepcidin production to sequester iron intracellularly as a means of depriving microorganisms of iron. Chronic inflammation may up-regulate hepcidin expression through the interleukin-6 (IL-6)-Janus kinase 2 (JAK2)-signal transducer and activator of transcription 3 (STAT3) pathway. The bone morphogenetic protein (BMP)-mothers against decapentaplegic homolog (SMAD) pathway is a major positive driver of hepcidin expression in response to either increased circulating iron in the form of transferrin or iron loading in organs. Hereditary hemochromatosis (HH) consists of several inherited disorders that cause inappropriately reduced hepcidin expression in response to body iron stores, leading to increased iron absorption from a normal diet. The most common form of HH is due to a mutation in the HFE gene, which causes a failure in the hepatocyte iron-sensing mechanism, leading to reduced hepcidin expression; the clinical manifestations of HFE-HH include increased serum transferrin-iron saturation and progressive iron loading in the liver and other tissues over time among patients who express the disease phenotype. In this article, we review the physiologic mechanisms and cellular pathways by which hepcidin expression is regulated, and the different forms of HH resulting from various mutations that cause hepcidin deficiency. We also review other drivers of hepcidin expression and the associated pathophysiologic consequences.

Hepatocyte growth factor protects PC12 cells against OGD/R-induced injury by reducing iron

In the light of hepatocyte growth factor (HGF) the inhibiting role on the expression of hepcidin, we hypothesized that HGF might be able to reduce cell and tissue iron by increasing ferroportin 1 (Fpn1) content and Fpn1-mediated iron release from cells and tissues. The hypothesized ability of HGF to reduce iron might be one of the mechanisms associated with its neuroprotective action under the conditions of ischemia/reperfusion (I/R). Here, we investigated the effects of HGF on the expression of hepcidin as well as transferrin receptor 1 (TfR1), divalent metal transporter 1 (DMT1), Fpn1, ferritin and iron regulatory proteins (IRPs) in oxygen-glucose deprivation and reoxygenation (OGD/R)-treated PC12 cells by real-time PCR and Western blot analysis. We demonstrated that HGF could completely reverse the OGD/R-induced reduction in Fpn1 and IRP1 expression and increase in ferritin light chain protein and hepcidin mRNA levels in PC12 cells. It was concluded that HGF protects PC12 cells against OGD/R-induced injury mainly by reducing cell iron contents via the up-regulation of Fpn1 and increased Fpn1-mediated iron export from cells. Our findings suggested that HGF may also be able to ameliorate OGD/R or I/R-induced overloading of brain iron by promoting Fpn1 expression.

Cell-type-specific insights into iron regulatory processes

Despite its essential role in many biological processes, iron is toxic when in excess due to its propensity to generate reactive oxygen species. To prevent diseases associated with iron deficiency or iron loading, iron homeostasis must be tightly controlled. Intracellular iron content is regulated by the Iron Regulatory Element-Iron Regulatory Protein (IRE-IRP) system, whereas systemic iron availability is adjusted to body iron needs chiefly by the hepcidin-ferroportin (FPN) axis. Here, we aimed to review advances in the field that shed light on cell-type-specific regulatory mechanisms that control or modify systemic and local iron balance, and how shifts in cellular iron levels may affect specialized cell functions.

Iron Homeostasis and Hepcidin Concentration in Patients With Acromegaly

Hepcidin is a protein responsible for maintaining iron (Fe) homeostasis. Data regarding the role of hepcidin in the pathomechanism of Fe balance disturbances associated with acromegaly (AG) are scarce. The aim of the study was to assess the impact of alterations in complete blood count parameters, Fe homeostasis, gonadal status and GH/IGF-1 on the level of hepcidin in AG patients. The study evaluated the differences in hepcidin concentration and iron homeostasis between patients newly diagnosed with AG in comparison to healthy control subjects (CS). We prospectively enrolled 25 adult patients newly diagnosed with AG and 25 healthy volunteers who served as CS. The level of hepcidin was measured using the Hepcidin 25 (bioactive) hs ELISA, which is a highly sensitive enzyme immunoassay for the quantitative in vitro diagnostic measurement (DRG Instruments GmbH, Germany). The median of hepcidin concentration in the serum of patients with AG was significantly lower 9.8 (6.2-18.2) ng/ml as compared to CS 21.3 (14.3-34.0) ng/ml (p = 0.003). In the AG group, a statistically significant negative correlation between hepcidin and IGF-1 (rho = -0.441) was observed. Our study demonstrated a decreased hepcidin level in AG patients in comparison to CS what may have a potentially protective effect against anemia through an increased bioavailability of Fe. Additionally, GH may have a positive direct or indirect effect on erythropoiesis. Further studies on larger patient groups are necessary in order to clarify the exact role of hepcidin in the regulation of erythropoiesis in the excess of GH/IGF-1.

Bone morphogenic proteins in iron homeostasis

The bone morphogenetic protein (BMP)-SMAD signaling pathway plays a central role in regulating hepcidin, which is the master hormone governing systemic iron homeostasis. Hepcidin is produced by the liver and acts on the iron exporter ferroportin to control iron absorption from the diet and iron release from body stores, thereby providing adequate iron for red blood cell production, while limiting the toxic effects of excess iron. BMP6 and BMP2 ligands produced by liver endothelial cells bind to BMP receptors and the coreceptor hemojuvelin (HJV) on hepatocytes to activate SMAD1/5/8 signaling, which directly upregulates hepcidin transcription. Most major signals that influence hepcidin production, including iron, erythropoietic drive, and inflammation, intersect with the BMP-SMAD pathway to regulate hepcidin transcription. Mutation or inactivation of BMP ligands, BMP receptors, HJV, SMADs or other proteins that modulate the BMP-SMAD pathway result in hepcidin dysregulation, leading to iron-related disorders, such as hemochromatosis and iron refractory iron deficiency anemia. Pharmacologic modulators of the BMP-SMAD pathway have shown efficacy in pre-clinical models to regulate hepcidin expression and treat iron-related disorders. This review will discuss recent insights into the role of the BMP-SMAD pathway in regulating hepcidin to control systemic iron homeostasis.

Hepcidin Status at 2 Months in Infants Fed Breast Milk Compared with Formula

INTRODUCTION

The basis for the superior absorption of iron from breast milk compared with infant formulas is unclear. The hormone hepcidin downregulates dietary iron absorption. Hepcidin production increases with increased body iron status (reflected in serum ferritin levels). We hypothesized that serum hepcidin levels are suppressed relative to iron status in infants fed breast milk compared with formula.

METHODS

Subjects were healthy infants presenting for routine 2-month clinic visit and strictly fed either breast milk or standard infant formula. Urinary hepcidin and ferritin levels (reflective of serum levels) were analyzed and compared across the breast milk- and formula-fed groups. The relationship between urinary hepcidin and ferritin levels within each group was analyzed by linear regression.

RESULTS

Twenty-four subjects were enrolled in each group. The median urinary hepcidin level in the group fed breast milk was lower than in formula (130 vs. 359 ng hepcidin/mg creatinine, p < 0.05). However, the median ferritin levels were similar (2.1 vs. 1.9 ng/mL). Within each group, urinary hepcidin correlated with urinary ferritin (r = 0.5, p < 0.05 for each group); however, the slope of the regression line was lower in the group fed breast milk compared with formula (p < 0.005).

CONCLUSION

Despite similar urinary ferritin levels, urinary hepcidin levels are lower at 2 months in infants fed breast milk compared with infants fed formula. Hepcidin levels correlate with iron status in each group; however, this relationship is relatively dampened in infants fed breast milk. We speculate that relatively lower infant hepcidin contributes to the superior efficiency of iron absorption from breast milk.

Expression of Iron-Regulatory Hormone Hepcidin and Iron Transporters Ferroportin and ZIP8 in Patients With and Without Chronic Rhinosinusitis

Airway epithelia express intrinsic antimicrobial and nutrient-sequestering factors, which contribute to the host defense of the respiratory tract. Hepcidin is an endogenous peptide hormone that serves as a key regulator of iron metabolism, and ferroportin and ZIP8 are iron transporters. All exhibit innate antimicrobial activity. The purpose of this pilot study is to determine if molecules involved in iron regulation are expressed within sinus epithelia and to compare levels of expression between patients with and without chronic rhinosinusitis (CRS). Sinus mucosa was obtained from patients with (n = 19) and without (n = 14) CRS. Real-time polymerase chain reaction following RNA extraction was used to quantify expression of hepcidin, ferroportin, and ZIP8 mRNA. Hepcidin, ferroportin, and ZIP8 were all detected in the sinus epithelia of patients with and without CRS. However, only ZIP8 was significantly changed in CRS, with a 2.5-fold mean increase in mRNA expression relative to controls ( P = .005). These findings suggest that ZIP8 may play a role in the innate epithelial defense of the paranasal sinuses.

Chenopodium Quinoa and Salvia Hispanica Provide Immunonutritional Agonists to Ameliorate Hepatocarcinoma Severity under a High-Fat Diet

Complex interactions between immunonutritional agonist and high fat intake (HFD), the immune system and finally gut microbiota are important determinants of hepatocarcinoma (HCC) severity. The ability of immunonutritional agonists to modulate major aspects such as liver innate immunity and inflammation and alterations in major lipids profile as well as gut microbiota during HCC development is poorly understood. ¹H NMR has been employed to assess imbalances in saturated fatty acids, MUFA and PUFA, which were associated to variations in iron homeostasis. These effects were dependent on the botanical nature (Chenopodium quinoa vs. Salvia hispanica L.) of the compounds. The results showed that immunonutritional agonists' promoted resistance to hepatocarcinogenesis under pro-tumorigenic inflammation reflected, at a different extent, in increased proportions of F4/80⁺ cells in injured livers as well as positive trends of accumulated immune mediators (CD68/CD206 ratio) in intestinal tissue. Administration of all immunonutritional agonists caused similar variations of fecal microbiota, towards a lower obesity-inducing potential than animals only fed a HFD. Modulation of Firmicutes to Bacteroidetes contents restored the induction of microbial metabolites to improve epithelial barrier function, showing an association with liver saturated fatty acids and the MUFA and PUFA fractions. Collectively, these data provide novel findings supporting beneficial immunometabolic effects targeting hepatocarcinogenesis, influencing innate immunity within the gut-liver axis, and providing novel insights into their immunomodulatory activity.

Androgens stimulate erythropoiesis through the DNA-binding activity of the androgen receptor in non-hematopoietic cells

BACKGROUND

Androgens function through DNA and non-DNA binding-dependent signalling of the androgen receptor (AR). How androgens promote erythropoiesis is not fully understood.

DESIGN AND METHODS

To identify the androgen signalling pathway, we treated male mice lacking the second zinc finger of the DNA-binding domain of the AR (AR^ΔZF2 ) with non-aromatizable 5α-dihydrotestosterone (5α-DHT) or aromatizable testosterone. To distinguish direct hematopoietic and non-hematopoietic mechanisms, we performed bone marrow reconstitution experiments.

RESULTS

In wild-type mice, 5α-DHT had greater erythroid activity than testosterone, which can be aromatized to estradiol. The erythroid response in wild-type mice following 5α-DHT treatment was associated with increased serum erythropoietin (EPO) and its downstream target erythroferrone, and hepcidin suppression. 5α-DHT had no erythroid activity in AR^ΔZF2 mice, proving the importance of DNA binding by the AR. Paradoxically, testosterone, but not 5α-DHT, suppressed EPO levels in AR^ΔZF2 mice, suggesting testosterone following aromatization may oppose the erythroid-stimulating effects of androgens. Female wild-type mice reconstituted with AR^ΔZF2 bone marrow cells remained responsive to 5α-DHT. In contrast, AR^ΔZF2 mice reconstituted with female wild-type bone marrow cells showed no response to 5α-DHT.

CONCLUSION

Erythroid promoting effects of androgens are mediated through DNA binding-dependent actions of the AR in non-hematopoietic cells, including stimulating EPO expression.

Ablation of Hepatocyte Smad1, Smad5, and Smad8 Causes Severe Tissue Iron Loading and Liver Fibrosis in Mice

A failure of iron to appropriately regulate liver hepcidin production is central to the pathogenesis of hereditary hemochromatosis. SMAD1/5 transcription factors, activated by bone morphogenetic protein (BMP) signaling, are major regulators of hepcidin production in response to iron; however, the role of SMAD8 and the contribution of SMADs to hepcidin production by other systemic cues remain uncertain. Here, we generated hepatocyte Smad8 single (Smad8^fl/fl ;Alb-Cre⁺ ), Smad1/5/8 triple (Smad158;Alb-Cre⁺ ), and littermate Smad1/5 double (Smad15;Alb-Cre⁺ ) knockout mice to investigate the role of SMAD8 in hepcidin and iron homeostasis regulation and liver injury. We found that Smad8;Alb-Cre⁺ mice exhibited no iron phenotype, whereas Smad158;Alb-Cre⁺ mice had greater iron overload than Smad15;Alb-Cre⁺ mice. In contrast to the sexual dimorphism reported for wild-type mice and other hemochromatosis models, hepcidin deficiency and extrahepatic iron loading were similarly severe in Smad15;Alb-Cre⁺ and Smad158;Alb-Cre⁺ female compared with male mice. Moreover, epidermal growth factor (EGF) failed to suppress hepcidin in Smad15;Alb-Cre⁺ hepatocytes. Conversely, hepcidin was still increased by lipopolysaccharide in Smad158;Alb-Cre⁺ mice, although lower basal hepcidin resulted in lower maximal hepcidin. Finally, unlike most mouse hemochromatosis models, Smad158;Alb-Cre⁺ developed liver injury and fibrosis at 8 weeks. Liver injury and fibrosis were prevented in Smad158;Alb-Cre⁺ mice by a low-iron diet and were minimal in iron-loaded Cre^- mice. Conclusion: Hepatocyte Smad1/5/8 knockout mice are a model of hemochromatosis that encompasses liver injury and fibrosis seen in human disease. These mice reveal the redundant but critical role of SMAD8 in hepcidin and iron homeostasis regulation, establish a requirement for SMAD1/5/8 in hepcidin regulation by testosterone and EGF but not inflammation, and suggest a pathogenic role for both iron loading and SMAD1/5/8 deficiency in liver injury and fibrosis.

Rapid growth is a dominant predictor of hepcidin suppression and declining ferritin in Gambian infants

Iron deficiency and iron deficiency anemia are highly prevalent in low-income countries, especially among young children. Hepcidin is the major regulator of systemic iron homeostasis. It controls dietary iron absorption, dictates whether absorbed iron is made available in circulation for erythropoiesis and other iron-demanding processes, and predicts response to oral iron supplementation. Understanding how hepcidin is itself regulated is therefore important, especially in young children. We investigated how changes in iron-related parameters, inflammation and infection status, seasonality, and growth influenced plasma hepcidin and ferritin concentrations during infancy using longitudinal data from two birth cohorts of infants in rural Gambia (n=114 and n=193). This setting is characterized by extreme seasonality, prevalent childhood anemia, undernutrition, and frequent infection. Plasma was collected from infants at birth and at regular intervals, up to 12 months of age. Hepcidin, ferritin and plasma iron concentrations declined markedly during infancy, with reciprocal increases in soluble transferrin receptor and transferrin concentrations, indicating declining iron stores and increasing tissue iron demand. In cross-sectional analyses at 5 and 12 months of age, we identified expected relationships of hepcidin with iron and inflammatory markers, but also observed significant negative associations between hepcidin and antecedent weight gain. Correspondingly, longitudinal fixed effects modeling demonstrated weight gain to be the most notable dynamic predictor of decreasing hepcidin and ferritin through infancy across both cohorts. Infants who grow rapidly in this setting are at particular risk of depletion of iron stores, but since hepcidin concentrations decrease with weight gain, they may also be the most responsive to oral iron interventions.

Review article: iron disturbances in chronic liver diseases other than haemochromatosis - pathogenic, prognostic, and therapeutic implications

BACKGROUND

Disturbances in iron regulation have been described in diverse chronic liver diseases other than hereditary haemochromatosis, and iron toxicity may worsen liver injury and outcome.

AIMS

To describe manifestations and consequences of iron dysregulation in chronic liver diseases apart from hereditary haemochromatosis and to encourage investigations that clarify pathogenic mechanisms, define risk thresholds for iron toxicity, and direct management METHODS: English abstracts were identified in PubMed by multiple search terms. Full length articles were selected for review, and secondary and tertiary bibliographies were developed.

RESULTS

Hyperferritinemia is present in 4%-65% of patients with non-alcoholic fatty liver disease, autoimmune hepatitis, chronic viral hepatitis, or alcoholic liver disease, and hepatic iron content is increased in 11%-52%. Heterozygosity for the C282Y mutation is present in 17%-48%, but this has not uniformly distinguished patients with adverse outcomes. An inappropriately low serum hepcidin level has characterised most chronic liver diseases with the exception of non-alcoholic fatty liver disease, and the finding has been associated mainly with suppression of transcriptional activity of the hepcidin gene. Iron overload has been associated with oxidative stress, advanced fibrosis and decreased survival, and promising therapies beyond phlebotomy and oral iron chelation have included hepcidin agonists.

CONCLUSIONS

Iron dysregulation is common in chronic liver diseases other than hereditary haemochromatosis, and has been associated with liver toxicity and poor prognosis. Further evaluation of iron overload as a co-morbid factor should identify the key pathogenic disturbances, establish the risk threshold for iron toxicity, and promote molecular interventions.

Signaling pathways regulating hepcidin

Since its discovery in 2001, there have been a number of important discoveries and findings that have increased our knowledge about the functioning of hepcidin. Hepcidin, the master iron regulator has been shown to be regulated by a number of physiological stimuli and their associated signaling pathways. This chapter will summarize our current understanding of how these physiological stimuli and downstream signaling molecules are involved in hepcidin modulation and ultimately contribute to the regulation of systemic or local iron homeostasis. The signaling pathways and molecules described here have been shown to primarily affect hepcidin at a transcriptional level, but these transcriptional changes correlate with changes in systemic iron levels as well, supporting the functional effects of hepcidin regulation by these signaling pathways.

Regulators of hepcidin expression

Iron, an essential nutrient, is required for many biological processes but is also toxic in excess. The lack of a mechanism to excrete excess iron makes it crucial for the body to regulate the amount of iron absorbed from the diet. This regulation is mediated by the hepatic hormone hepcidin. Hepcidin also controls iron release from macrophages that recycle iron and from hepatocytes that store iron. Hepcidin binds to the only known iron export protein, ferroportin, inducing its internalization and degradation and thus limiting the amount of iron released into the plasma. Important regulators of hepcidin, and therefore of systemic iron homeostasis, include plasma iron concentrations, body iron stores, infection and inflammation, hypoxia and erythropoiesis, and, to a lesser extent, testosterone. Dysregulation of hepcidin production contributes to the pathogenesis of many iron disorders: hepcidin deficiency causes iron overload in hereditary hemochromatosis and non-transfused β-thalassemia, whereas overproduction of hepcidin is associated with iron-restricted anemias seen in patients with chronic inflammatory diseases and inherited iron-refractory iron-deficiency anemia. The present review summarizes our current understanding of the molecular mechanisms and signaling pathways contributing to hepcidin regulation by these factors and highlights the issues that still need clarification.

Immunonutritional consequences of different serine-type protease inhibitors in a C57BL/6 hepatocarcinoma model

Imbalances in innate immunity and the activity of innate immune cells are implicated in the development of hepatocellular carcinoma (HCC). Plant seeds are good sources of protease inhibitors, which can have a significant influence on human health disorders, especially in the field of cancer prevention. To elucidate the impact and preventive effects of immunonutritional serine-type protease inhibitors (STPIs) on HCC, it was used an established model of chemically induced liver injury. Injured livers induced Akt as well as hepatic infiltration of NKG2D⁺ and CD74⁺ cells. Feeding STPIs reduced size and number of intrahepatic nodes of mononuclear. These animals showed an inverse association of the severity of HCC with bioactive hepcidin levels, which was significantly correlated with the hepatic myeloperoxidase activity. According to their origin, administration of STPIs significantly induce increased numbers of F4/80⁺ cells in injured livers that can be responsible for the biological effects detected on the parenchyma and inflammatory markers under DEN/TAA treatment. These findings can have direct implications in HCC immunotherapy where enhanced response(s) in inflammation-driven cancer patients could help promoting inflammation-driven processes and favor tumor growth. Altogether, this study demonstrates that oral administration of STPIs modulate innate immunity response influencing HCC aggressiveness and progression. These results represent a path forward to develop durable, long-lasting response against hepatocarcinoma and open a future research path in the development of coadjutant intervention strategies to pharmacological therapies.

MC-LR induces dysregulation of iron homeostasis by inhibiting hepcidin expression: A preliminary study

The liver is an important iron storage site and a primary MC-LR target. C57BL/6 and Hfe^-/- mice were used to investigate effects and mechanisms of MC-LR on systematic iron homeostasis. Body weight, tissue iron content, hematological and serological indexes, and histopathological were evaluated. Ultrastructure and iron metabolism-related genes and proteins were analyzed. MC-LR induced dose-dependent increases in red blood cells, hemoglobin, and hematocrit. In contrast MC-LR-induced dose-dependent decreases in mean corpuscular volume, hemoglobin, and hemoglobin concentration were observed both C57BL/6 and Hfe^-/- mice. In both mouse species, serological indexes increased. Aggravated liver and spleen iron were observed in C57BL/6 mice, consistent with Perls' Prussian blue staining. However, an opposite trend was observed in Hfe^-/- mice. C57BL/6 mice had lower Hamp1 (Hepcidn), Bmp6, Il-6, and Tmprss6. Significant increased Hjv, Hif-1α and Hif-2α were observed in both C57BL/6 and Hfe^-/- mice. MC-LR-induced pathological lesions were dose-dependent increase in C57BL/6 mice. More severe pathological injuries in MC-LR groups (25 μg/kg) were observed in Hfe^-/- mice than in C57BL/6 mice. In Hfe^-/- mice, upon exposure to 25 μg/kg MC-LR, mitochondrial membranes were damaged and mitochondrial counts increased with significant swelling. These results indicated that MC-LR can induce the accumulation of iron in C57BL/6 mice with the occurrence of anemia, similar to thalassemia. Moreover, dysregulation of iron homeostasis may be due to MC-LR-induced Hamp1 downregulation, possibly mediated by hypoxia or the IL6-STAT3 and BMP-SMAD signaling pathways.

Hepcidin regulation in a mouse model of acute hypoxia

OBJECTIVE

During hypoxia, hepcidin expression is inhibited to allow iron mobilization to sustain erythropoietic expansion. We analyzed molecular mechanisms underlying hypoxia-induced hepcidin inhibition in an in vivo model of acute hypoxia.

METHODS

Mice were kept under normal or hypoxic conditions for 6 hours and 15 hours and treated with α-PDGF-BB antibody or PDGF-BB receptor inhibitor. Blood, liver, spleen, and bone marrow were collected to extract RNA and protein or to quantify EPO and PDGF-BB. mRNA and protein levels were assessed by RT-PCR and Western blot.

RESULTS

Hepcidin was strongly inhibited at 15 hours, and this downregulation followed erythropoiesis activation and upregulation of several growth factors. PDGF-BB, erythroferrone, GDF15, and TWSG1 were upregulated by hypoxia in the bone marrow, but not in spleen or liver. Inactivation of PDGF-BB or its receptor suppressed the hypoxia-induced hepcidin inhibition.

CONCLUSION

Spleen and liver are not involved in the early stages of hypoxia-induced hepcidin downregulation. Our data support the role of PDGF-BB and probably also of erythroferrone in the recruitment of iron for erythropoiesis in the hypoxia setting. The rapid normalization of all the erythroid factors against persistent hepcidin suppression suggests that other signals are involved that should be clarified in future studies.

Do pregnancies reduce iron overload in HFE hemochromatosis women? results from an observational prospective study

Background

HFE hemochromatosis is an inborn error of iron metabolism linked to a defect in the regulation of hepcidin synthesis. This autosomal recessive disease typically manifests later in women than men. Although it is commonly stated that pregnancy is, with menses, one of the factors that offsets iron accumulation in women, no epidemiological study has yet supported this hypothesis. The aim of our study was to evaluate the influence of pregnancy on expression of the predominant HFE p.[Cys282Tyr];[Cys282Tyr] genotype.

Methods

One hundred and forty p.Cys282Tyr homozygous women enrolled in a phlebotomy program between 2004 and 2011 at a blood centre in western Brittany (France) were included in the study. After checking whether the disease expression was delayed in women than in men in our study, the association between pregnancy and iron overload was assessed using multivariable regression analysis.

Results

Our study confirms that women with HFE hemochromatosis were diagnosed later than men cared for during the same period (52.6 vs. 47.4 y., P < 0.001). Compared to no pregnancy, having at least one pregnancy was not associated with lower iron markers. In contrast, the amount of iron removed by phlebotomies appeared significantly higher in women who had at least one pregnancy (e^β = 1.50, P = 0.047). This relationship disappeared after adjustment for confounding factors (e^β = 1.35, P = 0.088).

Conclusions

Our study shows that pregnancy status has no impact on iron markers level, and is not in favour of pregnancy being a protective factor in progressive iron accumulation. Our results are consistent with recent experimental data suggesting that the difference in disease expression observed between men and women may be explained by other factors such as hormones.

Quercetin and iron metabolism: What we know and what we need to know

Iron is a life-supporting micronutrient that is required in the human diet, and is essential for maintaining physiological homeostasis. Properly harnessing a redox-active metal such as iron is a great challenge for cells and organisms because an excess of highly reactive iron catalyzes the formation of reactive oxygen species and can lead to cell and tissue damage. Quercetin is a typical flavonoid that is commonly found in fruits and vegetables and has versatile biological effects. From a classical viewpoint, owing to its unique chemical characteristics, quercetin has long been associated with iron metabolism only in the context of its iron-chelating and ROS-scavenging activities. However, within the field of human iron biology, expanding concepts of the roles of quercetin are flourishing, and great strides are being made in understanding the interactions between quercetin and iron. This progress highlights the varied roles of quercetin in iron metabolism, which involve much more than iron chelation alone. A review of these studies provides an ideal context to summarize recent progress and discuss compelling evidence for therapeutic opportunities that could arise from a better understanding of the underlying mechanisms.

Differential regulation of hepcidin in cancer and non-cancer tissues and its clinical implications

Hepcidin is a crucial peptide for regulating cellular iron efflux. Because iron is essential for cell survival, especially for highly active cells, such as tumor cells, it is imperative to understand how tumor cells manipulate hepcidin expression for their own metabolic needs. Studies suggest that hepcidin expression and regulation in tumor cells show important differences in comparison with those in non-tumorous cells. These differences should be investigated to develop new strategies to fight cancer cells. Manipulating hepcidin expression to starve cancer cells for iron may prove to be a new therapy in the anticancer arsenal.

Baseline IL-2 and the AIH score can predict the response to standard therapy in paediatric autoimmune hepatitis

Although autoimmune hepatitis (AIH) can be treated with corticosteroid-based first-line therapy, incomplete remission is associated with progressive liver fibrosis. So far accepted predictors of the subsequent treatment response of AIH patients are lacking. Therefore, we analysed baseline parameters, including iron homeostasis and cytokine levels, in 60 children with paediatric AIH (pAIH). In contrast to adults, elevated serum markers indicating iron overload were not commonly found in children. Therefore, ferritin was not predictive of the treatment response in pAIH. Although baseline immunoglobulins were lower in pAIH children with subsequent complete biochemical remission (BR) upon standard first-line therapy, only lower AIH scores (≤16 points) could predict BR upon standard therapy in our training and validation cohorts. Additionally, higher baseline IL-2 and MCP-1/CCL2 levels were associated with BR in a sub-cohort. A combined score of IL-2 level and a simplified AIH score predicted treatment response more precisely than both parameter alone in this sub-cohort. In conclusion, the baseline AIH score could be validated as a predictor of treatment response in pAIH. Additionally, low baseline IL-2 may help identify children who need salvage therapy. This could be important because the use of low-dose IL-2 therapies is being tested in various autoimmune diseases.

Uncoupled iron homeostasis in type 2 diabetes mellitus

Diabetes mellitus is frequently associated with iron overload conditions, such as primary and secondary hemochromatosis. Conversely, patients affected by type 2 diabetes mellitus (T2DM) show elevated ferritin levels, a biomarker for increased body iron stores. Despite these documented associations between dysregulated iron metabolism and T2DM, the underlying mechanisms are poorly understood. Here, we show that T2DM patients have reduced serum levels of hepcidin, the iron-regulated hormone that maintains systemic iron homeostasis. Consistent with this finding, we also observed an increase in circulating iron and ferritin levels. Our analysis of db/db mice demonstrates that this model recapitulates the systemic alterations observed in patients. Interestingly, db/db mice show an overall hepatic iron deficiency despite unaltered expression of ferritin and the iron importer TfR1. In addition, the liver correctly senses increased circulating iron levels by activating the BMP/SMAD signaling pathway even though hepcidin expression is decreased. We show that increased AKT phosphorylation may override active BMP/SMAD signaling and decrease hepcidin expression in 10-week old db/db mice. We conclude that the metabolic alterations occurring in T2DM impact on the regulation of iron homeostasis on multiple levels. As a result, metabolic perturbations induce an "iron resistance" phenotype, whereby signals that translate increased circulating iron levels into hepcidin production, are dysregulated.

KEY MESSAGES

T2DM patients show increased circulating iron levels. T2DM is associated with inappropriately low hepcidin levels. Metabolic alterations in T2DM induce an "iron resistance" phenotype.

Hyperferritinemia and hypergammaglobulinemia predict the treatment response to standard therapy in autoimmune hepatitis

Autoimmune hepatitis (AIH) is a chronic hepatitis with an increasing incidence. The majority of patients require life-long immunosuppression and incomplete treatment response is associated with a disease progression. An abnormal iron homeostasis or hyperferritinemia is associated with worse outcome in other chronic liver diseases and after liver transplantation. We assessed the capacity of baseline parameters including the iron status to predict the treatment response upon standard therapy in 109 patients with untreated AIH type 1 (AIH-1) in a retrospective single center study. Thereby, a hyperferritinemia (> 2.09 times upper limit of normal; Odds ratio (OR) = 8.82; 95% confidence interval (CI): 2.25–34.52) and lower immunoglobulins (<1.89 times upper limit of normal; OR = 6.78; CI: 1.87–24.59) at baseline were independently associated with the achievement of complete biochemical remission upon standard therapy. The predictive value increased when both variables were combined to a single treatment response score, when the cohort was randomly split into a training (area under the curve (AUC) = 0.749; CI 0.635–0.863) and internal validation cohort (AUC = 0.741; CI 0.558–0.924). Patients with a low treatment response score (<1) had significantly higher cumulative remission rates in the training (p<0.001) and the validation cohort (p = 0.024). The baseline hyperferritinemia was accompanied by a high serum iron, elevated transferrin saturations and mild hepatic iron depositions in the majority of patients. However, the abnormal iron status was quickly reversible under therapy. Mechanistically, the iron parameters were not stringently related to a hepatocellular damage. Ferritin rather seems deregulated from the master regulator hepcidin, which was down regulated, potentially mediated by the elevated hepatocyte growth factor. In conclusion, baseline levels of serum ferritin and immunoglobulins, which are part of the diagnostic work-up of AIH, can be used to predict the treatment response upon standard therapy in AIH-1, although confirmation from larger multicenter studies is pending.

A Red Carpet for Iron Metabolism

200 billion red blood cells (RBCs) are produced every day, requiring more than 2 × 10¹⁵ iron atoms every second to maintain adequate erythropoiesis. These numbers translate into 20 mL of blood being produced each day, containing 6 g of hemoglobin and 20 mg of iron. These impressive numbers illustrate why the making and breaking of RBCs is at the heart of iron physiology, providing an ideal context to discuss recent progress in understanding the systemic and cellular mechanisms that underlie the regulation of iron homeostasis and its disorders.

Imatinib and spironolactone suppress hepcidin expression

Disorders of iron metabolism are largely attributed to an excessive or insufficient expression of hepcidin, the master regulator of systemic iron homeostasis. Here, we investigated whether drugs targeting genetic regulators of hepcidin can affect iron homeostasis. We focused our efforts on drugs approved for clinical use to enable repositioning strategies and/or to reveal iron-related side effects of widely prescribed therapeutics. To identify hepcidin-modulating therapeutics, we re-evaluated data generated by a genome-wide RNAi screen for hepcidin regulators. We identified ‘druggable’ screening hits and validated those by applying RNAi of potential drug targets and small-molecule testing in a hepatocytic cell line, in primary murine and human hepatocytes and in mice. We initially identified spironolactone, diclofenac, imatinib and Suberoylanilide hydroxamic acid (SAHA) as hepcidin modulating drugs in cellular assays. Among these, imatinib and spironolactone further suppressed liver hepcidin expression in mice. Our results demonstrate that a commonly used anti-hypertensive drug, spironolactone, which is prescribed for the treatment of heart failure, acne and female hirsutism, as well as imatinib, a first-line, lifelong therapeutic option for some frequent cancer types suppress hepcidin expression in cultured cells and in mice. We expect these results to be of relevance for patient management, which needs to be addressed in prospective clinical studies.

Regulation of the Iron Homeostatic Hormone Hepcidin

Iron is required for many biological processes but is also toxic in excess; thus, body iron balance is maintained through sophisticated regulatory mechanisms. The lack of a regulated iron excretory mechanism means that body iron balance is controlled at the level of absorption from the diet. Iron absorption is regulated by the hepatic peptide hormone hepcidin. Hepcidin also controls iron release from cells that recycle or store iron, thus regulating plasma iron concentrations. Hepcidin exerts its effects through its receptor, the cellular iron exporter ferroportin. Important regulators of hepcidin, and therefore of systemic iron homeostasis, include plasma iron concentrations, body iron stores, infection and inflammation, and erythropoiesis. Disturbances in the regulation of hepcidin contribute to the pathogenesis of many iron disorders: hepcidin deficiency causes iron overload in hereditary hemochromatosis and nontransfused β-thalassemia, whereas overproduction of hepcidin is associated with iron-restricted anemias seen in patients with chronic kidney disease, chronic inflammatory diseases, some cancers, and inherited iron-refractory iron deficiency anemia. This review summarizes our current understanding of the molecular mechanisms and signaling pathways involved in the control of hepcidin synthesis in the liver, a principal determinant of plasma hepcidin concentrations.

Hepcidin inhibits Smad3 phosphorylation in hepatic stellate cells by impeding ferroportin-mediated regulation of Akt

Hepatic stellate cell (HSC) activation on liver injury facilitates fibrosis. Hepatokines affecting HSCs are largely unknown. Here we show that hepcidin inhibits HSC activation and ameliorates liver fibrosis. We observe that hepcidin levels are inversely correlated with exacerbation of fibrosis in patients, and also confirm the relationship in animal models. Adenoviral delivery of hepcidin to mice attenuates liver fibrosis induced by CCl₄ treatment or bile duct ligation. In cell-based assays, either hepcidin from hepatocytes or exogenous hepcidin suppresses HSC activation by inhibiting TGFβ1-mediated Smad3 phosphorylation via Akt. In activated HSCs, ferroportin is upregulated, which can be prevented by hepcidin treatment. Similarly, ferroportin knockdown in HSCs prohibits TGFβ1-inducible Smad3 phosphorylation and increases Akt phosphorylation, whereas ferroportin over-expression has the opposite effect. HSC-specific ferroportin deletion also ameliorates liver fibrosis. In summary, hepcidin suppresses liver fibrosis by impeding TGFβ1-induced Smad3 phosphorylation in HSCs, which depends on Akt activated by a deficiency of ferroportin.

The peptide hormone hepcidin is released from hepatocytes and regulates iron homoeostasis. Here, the authors show that hepcidin also regulates the activation of hepatic stellate cells (HSCs) in mouse models of liver fibrosis by reducing ferroportin expression and inhibiting the HSC response to TGFβ.

Correlates of serum hepcidin levels and its association with cardiovascular disease in an elderly general population

BACKGROUND

The expression of the key iron regulatory hormone hepcidin is regulated by iron availability, inflammation, hormones, hypoxia, and anaemia. Increased serum concentrations of hepcidin have recently been linked to atherosclerosis. We studied demographic, haematologic, biochemical, and dietary correlates of serum hepcidin levels and its associations with incident cardiovascular disease and with carotid atherosclerosis.

METHODS

Serum hepcidin concentrations were measured by tandem mass spectrometry in samples taken in 2000 from 675 infection-free participants of the prospective population-based Bruneck study (age, mean±standard deviation, 66.0±10.2; 48.1% male). Blood parameters were measured by standard methods. Dietary intakes of iron and alcohol were surveyed with a food frequency questionnaire. Carotid atherosclerosis (365 cases) was assessed by ultrasound and subjects were observed for incident stroke, myocardial infarction, or sudden cardiac death (91 events) until 2010.

RESULTS

Median (interquartile range) hepcidin levels were 2.27 nM (0.86, 4.15). Most hepcidin correlates were in line with hepcidin as an indicator of iron stores. Independently of ferritin, hepcidin was related directly to physical activity (p=0.024) and fibrinogen (p<0.0001), and inversely to alcohol intake (p=0.006), haemoglobin (p=0.027), and γ-glutamyltransferase (p<0.0001). Hepcidin and hepcidin-to-ferritin ratio were not associated with prevalent carotid atherosclerosis (p=0.43 and p=0.79) or with incident cardiovascular disease (p=0.62 and p=0.33).

CONCLUSIONS

In this random sample of the general community, fibrinogen and γ-glutamyltransferase were the most significant hepcidin correlates independent of iron stores, and hepcidin was related to neither atherosclerosis nor cardiovascular disease.

The Repair of Skeletal Muscle Requires Iron Recycling through Macrophage Ferroportin

Macrophages recruited at the site of sterile muscle damage play an essential role in the regeneration of the tissue. In this article, we report that the selective disruption of macrophage ferroportin (Fpn) results in iron accumulation within muscle-infiltrating macrophages and jeopardizes muscle healing, prompting fat accumulation. Macrophages isolated from the tissue at early time points after injury express ferritin H, CD163, and hemeoxygenase-1, indicating that they can uptake heme and store iron. At later time points they upregulate Fpn expression, thus acquiring the ability to release the metal. Transferrin-mediated iron uptake by regenerating myofibers occurs independently of systemic iron homeostasis. The inhibition of macrophage iron export via the silencing of Fpn results in regenerating muscles with smaller myofibers and fat accumulation. These results highlight the existence of a local pathway of iron recycling that plays a nonredundant role in the myogenic differentiation of muscle precursors, limiting the adipose degeneration of the tissue.

New insights into iron regulation and erythropoiesis

PURPOSE OF REVIEW

Iron homeostasis and erythropoiesis regulate each other to ensure optimal delivery of oxygen and iron to cells and tissues. Defining the mechanisms of this crosstalk is important for understanding the pathogenesis of common conditions associated with disordered iron metabolism and erythropoiesis.

RECENT FINDINGS

Stress erythropoiesis causes suppression of hepcidin to increase iron availability for hemoglobin synthesis. The erythroid hormone erythroferrone (ERFE) was identified as the mediator of this process. ERFE and additional candidates (TWSG1 and GDF15) may also mediate hepcidin suppression in ineffective erythropoiesis. Several mechanisms by which iron regulates erythropoiesis were also recently identified. Iron deficiency suppresses erythropoietin production via the IRP1-HIF2α axis to prevent excessive iron usage by erythropoiesis during systemic iron restriction. Iron restriction also directly impairs erythroid maturation by inhibiting aconitase, and this can be reversed by the administration of the aconitase product isocitrate. Another novel target is GDF11, which is thought to autoinhibit erythroid maturation. GDF11 traps show promising pharmacologic activity in models of both ineffective erythropoiesis and iron-restricted anemia.

SUMMARY

This review summarizes exciting advances in understanding the mechanisms of iron and erythropoietic regulation, and development of novel therapeutic tools for disorders resulting from dysregulation of iron metabolism or erythropoiesis.

Iron and the liver

Humans have evolved to retain iron in the body and are exposed to a high risk of iron overload and iron-related toxicity. Excess iron in the blood, in the absence of increased erythropoietic needs, can saturate the buffering capacity of serum transferrin and result in non-transferrin-bound highly reactive forms of iron that can cause damage, as well as promote fibrogenesis and carcinogenesis in the parenchymatous organs. A number of hereditary or acquired diseases are associated with systemic or local iron deposition or iron misdistribution in organs or cells. Two of these, the HFE- and non-HFE hemochromatosis syndromes represent the paradigms of genetic iron overload. They share common clinical features and the same pathogenic basis, in particular, a lack of synthesis or activity of hepcidin, the iron hormone. Before hepcidin was discovered, the liver was simply regarded as the main site of iron storage and, as such, the main target of iron toxicity. Now, as the main source of hepcidin, it appears that the loss of the hepcidin-producing liver mass or genetic and acquired factors that repress hepcidin synthesis in the liver may also lead to iron overload. Usually, there is low-grade excess iron which, through oxidative stress, is sufficient to worsen the course of the underlying liver disease or other chronic diseases that are apparently unrelated to iron, such as chronic metabolic and cardiovascular diseases. In the future, modulation of hepcidin synthesis and activity or hepcidin hormone-replacing strategies may become therapeutic options to cure iron-related disorders.

Modulation of hepcidin to treat iron deregulation: potential clinical applications

The secreted peptide hormone hepcidin regulates systemic and local iron homeostasis through degradation of the iron exporter ferroportin. Dysregulation of hepcidin leads to altered iron homeostasis and development of pathological disorders including hemochromatosis, and iron loading and iron restrictive anemias. Therapeutic modulation of hepcidin is a promising method to ameliorate these conditions. Several approaches have been taken to enhance or reduce the effects of hepcidin in vitro and in vivo. Based on these approaches, hepcidin modulating drugs have been developed and are undergoing clinical evaluation. In this article we review the rationale for development of these drugs, the data concerning their safety and efficacy, their therapeutic uses, and potential future prospects.

Increased hepcidin in transferrin-treated thalassemic mice correlates with increased liver BMP2 expression and decreased hepatocyte ERK activation

Iron overload results in significant morbidity and mortality in β-thalassemic patients. Insufficient hepcidin is implicated in parenchymal iron overload in β-thalassemia and approaches to increase hepcidin have therapeutic potential. We have previously shown that exogenous apo-transferrin markedly ameliorates ineffective erythropoiesis and increases hepcidin expression in Hbb(th1/th1) (thalassemic) mice. We utilize in vivo and in vitro systems to investigate effects of exogenous apo-transferrin on Smad and ERK1/2 signaling, pathways that participate in hepcidin regulation. Our results demonstrate that apo-transferrin increases hepcidin expression in vivo despite decreased circulating and parenchymal iron concentrations and unchanged liver Bmp6 mRNA expression in thalassemic mice. Hepatocytes from apo-transferrin-treated mice demonstrate decreased ERK1/2 pathway and increased serum BMP2 concentration and hepatocyte BMP2 expression. Furthermore, hepatocyte ERK1/2 phosphorylation is enhanced by neutralizing anti-BMP2/4 antibodies and suppressed in vitro in a dose-dependent manner by BMP2, resulting in converse effects on hepcidin expression, and hepatocytes treated with MEK/ERK1/2 inhibitor U0126 in combination with BMP2 exhibit an additive increase in hepcidin expression. Lastly, bone marrow erythroferrone expression is normalized in apo-transferrin treated thalassemic mice but increased in apo-transferrin injected wild-type mice. These findings suggest that increased hepcidin expression after exogenous apo-transferrin is in part independent of erythroferrone and support a model in which apo-transferrin treatment in thalassemic mice increases BMP2 expression in the liver and other organs, decreases hepatocellular ERK1/2 activation, and increases nuclear Smad to increase hepcidin expression in hepatocytes.