Hepcidin decreases iron transporter expression in vivo in mouse duodenum and spleen and in vitro in THP-1 macrophages and intestinal Caco-2 cells

Protective effect of Angelica sinensis polysaccharide on pregnant rats suffering from iron deficiency anemia via regulation of the hepcidin-FPN1 axis

Iron deficiency anemia (IDA) is a common micronutrient deficiency among pregnant women with deleterious maternal and fetal outcomes. Angelica sinensis polysaccharide (ASP) has been shown to reduce hepcidin expression in IDA rats. However, the role of ASP in the treatment of IDA during pregnancy and its potential mechanisms have not been investigated. Moreover, the effect of ASP on duodenal iron absorption is not clear. The aim of this study was to investigate the preventive efficacy of ASP against IDA during pregnancy and clarify the underlying mechanisms. Our results showed that ASP improved maternal hematological parameters, increased serum iron, maternal tissue iron, and fetal liver iron content, and improved pregnancy outcomes. Additionally, ASP combated oxidative stress caused by iron deficiency by improving the body's antioxidant capacity. Western blot results demonstrated that ASP downregulated hepcidin expression by blocking the BMP6/SMAD4, JAK2/STAT3 and TfR2/HFE signaling pathways, which in turn increased the expression of FPN1 in the liver, spleen, and duodenum and promoted iron cycling in the body. Furthermore, ASP increased the expression of DMT1 and Dcytb in the duodenum, thereby facilitating duodenal iron uptake. Our results suggest that ASP is a potential agent for the prevention and treatment of IDA during pregnancy.

Prevalence of anemia and related nutrient deficiencies after sleeve gastrectomy: A systematic review and meta-analysis

This study aimed to investigate the prevalence of anemia and related nutrient deficiencies after sleeve gastrectomy (SG). Four online databases were searched for relevant articles. Thirty-one studies with 7639 patients were included in the meta-analysis. The pooled anemia prevalence was 7%, 6%, 9%, 10%, 12%, 25%, 20%, and 18% at baseline, 3 months, 6 months, 12 months, 24 months, 36 months, 48 months, and 60 months, respectively. Although the prevalence of vitamin B12 and folate deficiencies remained low postoperatively, the prevalence of ferritin deficiency steadily increased from 6% at baseline to 27% at 60 months. The prevalence of serum iron deficiency decreased from 13% at baseline to 6% at 24 months and increased to 20% at 60 months. Anemia and ferritin deficiency were strongly correlated (Pearson correlation coefficient = 0.774, p = 0.041). Subgroup analysis suggested that age ≤40 years, preoperative anemia, and insufficient iron supplementations were high-risk factors for postoperative anemia. SG is associated with an increased risk of anemia and decreased iron storage over long-term observation. Routine iron supplementations may reduce anemia after SG; however, the dosages recommended by current guidelines may be insufficient. More strict monitoring schedules and supplementation strategies should be established for the timely detection and management of postoperative anemia.

HCV-Induced Immunometabolic Crosstalk in a Triple-Cell Co-Culture Model Capable of Simulating Systemic Iron Homeostasis

Iron is crucial to the regulation of the host innate immune system and the outcome of many infections. Hepatitis C virus (HCV), one of the major viral human pathogens that depends on iron to complete its life cycle, is highly skilled in evading the immune system. This study presents the construction and validation of a physiologically relevant triple-cell co-culture model that was used to investigate the input of iron in HCV infection and the interplay between HCV, iron, and determinants of host innate immunity. We recorded the expression patterns of key proteins of iron homeostasis involved in iron import, export and storage and examined their relation to the iron regulatory hormone hepcidin in hepatocytes, enterocytes and macrophages in the presence and absence of HCV. We then assessed the transcriptional profiles of pro-inflammatory cytokines Interleukin-6 (IL-6) and interleukin-15 (IL-15) and anti-inflammatory interleukin-10 (IL-10) under normal or iron-depleted conditions and determined how these were affected by infection. Our data suggest the presence of a link between iron homeostasis and innate immunity unfolding among liver, intestine, and macrophages, which could participate in the deregulation of innate immune responses observed in early HCV infection. Coupled with iron-assisted enhanced viral propagation, such a mechanism may be important for the establishment of viral persistence and the ensuing chronic liver disease.

Iron Transporter Protein Expressions in Children with Celiac Disease

Anemia is a frequent finding in children with celiac disease but the detailed pathophysiological mechanisms in the intestine remain obscure. One possible explanation could be an abnormal expression of duodenal iron transport proteins. However, the results have so far been inconsistent. We investigated this issue by comparing immunohistochemical stainings of duodenal cytochrome B (DCYTB), divalent metal transporter 1 (DMT1), ferroportin, hephaestin and transferrin receptor 1 (TfR1) in duodenal biopsies between 27 children with celiac disease and duodenal atrophy, 10 celiac autoantibody-positive children with potential celiac disease and six autoantibody-negative control children. Twenty out of these 43 subjects had anemia. The expressions of the iron proteins were investigated with regard to saturation and the percentage of the stained area or stained membrane length of the enterocytes. The results showed the stained area of ferroportin to be increased and the saturation of hephaestin to be decreased in celiac disease patients compared with controls. There were no differences in the transporter protein expressions between anemic and non-anemic patients. The present results suggest an iron status-independent alteration of ferroportin and hephaestin proteins in children with histologically confirmed celiac disease.

The hematologic consequences of obesity

The prevalence of obesity is increasing and progressively influencing physician-patient interactions. While there is a sizable amount of data demonstrating that obesity is a state of low-grade inflammation, to our knowledge, there is no single review summarizing its effects on hematologic parameters and thrombotic risk. We performed a literature search which largely surfaced observational studies, with a few systematic reviews and meta-analyses of these studies. We took care to review the mechanisms driving an inflammatory state and obesity's effect on white blood cells, red blood cells, platelets, and thrombotic risk. There is an observed relative, and sometimes absolute leukocytosis driven by this inflammatory state. Obesity is also associated with increased platelet counts and an increased risk for venous thromboembolism (VTE). Lastly, the association between obesity, iron deficiency (ID), and red blood cell counts may be present but remains uncertain. Recognizing the above associations may provide clinicians with reassurance regarding otherwise unexplained hematologic abnormalities in obese individuals. We hope this review will prompt future studies to further understand the underlying mechanisms driving these abnormalities and identify modifiable risk factors and potential therapeutic targets to prevent the development of probable obesity-associated conditions with significant morbidity and mortality, such as ID and VTE.

Expression of iron regulatory proteins in full-term swine placenta

In swine, even though the pregnant sows were with iron abundance, the inborn iron reserve of piglets was compromised. This indicates the insufficiency of molecular machinery involved in local placental iron flux. Here, we investigated the expression of iron regulatory proteins like hepcidin and ferroportin and also their association with iron reserve, inflammation and oxidative stress in placenta of full-term pregnant sows (n = 6). Amplification and sequencing of placental DNA confirmed the presence of hepcidin (MN579557) and ferroportin (MN565887) sequences and their 100% identity with existing GenBank data. Real-time amplification of placental mRNA revealed significant higher expression of hepcidin (p < .05) than ferroportin. Western blot analysis of placental tissues revealed specific bands for both hepcidin (~8 kDa) and ferroportin (~62 kDa) molecules. Immunohistochemistry revealed the immunoreactivity for both proteins in the cytoplasm and membrane of trophoblastic cells of the placenta. Hepcidin and ferroportin expressions were positively associated with placental non-haem iron reserve (p < .0001; p = .033), lipid peroxidation (p = .0060; p < .0001) and reactive oxygen species level (p = .0092; p = .0292). Hepcidin expression was positively associated with interleukin - 6 (p = .0002) and interferon gamma (p < .0001) expressions but ferroportin expression was negatively associated with interleukin-6 (p = .0005), interleukin-1β (p = .0226) and interferon gamma (p = .0059) expressions. This indicates hepcidin and ferroportin may have a role in controlling the local placental iron flux by acting as a molecular bridge between iron trafficking and inflammation.

Iron Absorption in Celiac Disease and Nutraceutical Effect of 7-Hydroxymatairesinol. Mini-Review

Anemia is the main extra-gastrointestinal symptom in inflammatory bowel diseases (IBDs). Interleukin-6 (IL-6) and other cytokines are secreted and act in the microenvironment of the small intestine mucous membrane of IBD patients. Iron is essential for multiple cell functions and its homeostasis is regulated by the hepcidin–ferroportin axis. Hepcidin (HEPC) is mainly produced by the liver in response to iron needs but is also an acute phase protein. During inflammation, hepcidin is upregulated by IL-6 and is responsible for iron compartmentalization within cells, in turn causing anemia of inflammation. Tissues other than liver can produce hepcidin in response to inflammatory stimuli, in order to decrease iron efflux at a local level, then acting in an autocrine–paracrine manner. In IBDs and, in particular, in celiac disease (CeD), IL-6 might trigger the expression, upregulation and secretion of hepcidin in the small intestine, reducing iron efflux and exacerbating defective iron absorption. 7-Hydroxymatairesinol (7-HMR) belongs to the family of lignans, polyphenolic compounds produced by plants, and has nutraceutical antioxidant, anti-inflammatory and estrogenic properties. In this mini-review we revise the role of inflammation in IBDs and in particular in CeD, focusing our attention on the close link among inflammation, anemia and iron metabolism. We also briefly describe the anti-inflammatory and estrogenic activity of 7-HMR contained in foods that are often consumed by CeD patients. Finally, considering that HEPC expression is regulated by iron needs, inflammation and estrogens, we explored the hypothesis that 7-HMR consumption could ameliorate anemia in CeD using Caco-2 cells as bowel model. Further studies are needed to verify the regulation pathway through which 7-HMR may interfere with the local production of HEPC in bowel.

Regulation of tissue iron homeostasis: the macrophage "ferrostat"

Iron is an essential element for multiple fundamental biological processes required for life; yet iron overload can be cytotoxic. Consequently, iron concentrations at the cellular and tissue level must be exquisitely governed by mechanisms that complement and fine-tune systemic control. It is well appreciated that macrophages are vital for systemic iron homeostasis, supplying or sequestering iron as needed for erythropoiesis or bacteriostasis, respectively. Indeed, recycling of iron through erythrophagocytosis by splenic macrophages is a major contributor to systemic iron homeostasis. However, accumulating evidence suggests that tissue-resident macrophages regulate local iron availability and modulate the tissue microenvironment, contributing to cellular and tissue function. Here, we summarize the significance of tissue-specific regulation of iron availability and highlight how resident macrophages are critical for this process. This tissue-dependent regulation has broad implications for understanding both resident macrophage function and tissue iron homeostasis in health and disease.

The Short Tandem Repeat of the DMT1 Gene as a Molecular Marker of Elite Long-Distance Runners

The DMT1 gene encodes divalent metal transporter 1, a membrane iron transport protein. Divalent metal transporter 1 influences cellular iron availability, which might further affect aerobic exercise capacity. Short tandem repeat (STR) polymorphisms have been used as genetic markers in the literature, yet the STR polymorphisms of the DMT1 gene have not been well studied. In this current study, we explored the polymorphisms of the DMT1 gene in a group of elite long-distance runners and controls, by using the PCR-RFLP (Restriction Fragment Length Polymorphism) and Gene scan technology. We found that the genotype frequency of the homozygous 258 bp STR polymorphism of the DMT1 gene (258 bp/258 bp) was significantly higher in the athlete group than in the controls (χ² = 14.01, p = 0.006) so does the allele frequency of the 258 bp STR polymorphism (χ² = 12.867, p = 0.008). These data suggested that the STR polymorphism of the DMT1 gene might be correlated with aerobic exercise capacity and the 258 bp homozygous (25 bp/258 bp) could be used as a molecular marker for the talent identification of elite long-distance runners.

Extrahepatic hepcidin production: The intriguing outcomes of recent years

Hepcidin is the hyposideremic hormone regulating iron metabolism. It is a defensin-like disulfide-bonded peptide with antimicrobial activity. The main site of hepcidin production is the liver where its synthesis is modulated by iron, inflammation and erythropoietic signaling. However, hepcidin locally produced in several peripheral organs seems to be an important actor for the maintenance of iron homeostasis in these organs. This review highlights the presence of peripheral hepcidin and its potential functions. Understanding the role of extrahepatic hepcidin could be of great physiological and therapeutic importance for several specific pathologies.

Protective Role of Hepcidin in Polymicrobial Sepsis and Acute Kidney Injury

Background: Acute kidney injury (AKI) portends worse prognosis following sepsis, with limited available interventions. Host iron acquisition by pathogens and systemic inflammatory response are key events in the pathogenesis of sepsis. In sepsis, hepcidin induces iron sequestration to limit iron availability to pathogens. Hepcidin is also known to limit inflammation. Since its role in pathophysiology of sepsis-associated AKI is unknown, we investigated the effect of exogenous hepcidin in endotoxin- and peritonitis-induced pathology and AKI.

Methods: C57BL/6 mice were treated with saline or 50–100 µg of hepcidin, pre- and post-LPS injection, or cecal ligation and puncture (CLP, model of peritonitis). Splenectomized mice were challenged with LPS, with and without hepcidin. Mice were euthanized at 24 h after LPS injection and at different time points after CLP. Systemic inflammation and renal injury markers were assessed. Direct effect of hepcidin on renal tubular and endothelial cells was evaluated using endotoxin-induced cytotoxic serum. Role of heavy chain ferritin (H-ferritin) in mediating hepcidin-induced anti-inflammatory effect on LPS stimulated macrophages was evaluated with siRNA studies.

Results: Twenty-four hours pretreatment with hepcidin significantly reduced LPS-induced AKI. Hepcidin ameliorated LPS-induced increase in serum TNFα and renal Cox-2, and prevented loss in PGC1α and cytochrome c oxidase activity. This was associated with reduced glomerular injury and preserved mitochondrial structure. Hepcidin did not exert direct protection on the renal parenchymal cells but reduced endotoxin-induced serum cytotoxicity to mitigate renal injury. Splenectomy reduced LPS-induced early inflammation and AKI, independent of hepcidin, indicating the importance of systemic inflammation. Higher splenic H-ferritin in hepcidin-treated animals was associated with reduced splenocytes apoptosis and inflammation. Hepcidin reduced LPS-induced IL-6 secretion in macrophages in H-ferritin dependent manner. Hepcidin significantly reduced CLP-induced AKI, and mortality (20% hepcidin treated vs 80% PBS treated). Importantly hepcidin reduced bacteremia and AKI even when administered after onset of sepsis.

Conclusion: We demonstrate a protective role of hepcidin in endotoxin- and peritonitis-induced pathologies and AKI, exerted primarily through its anti-inflammatory effects, and antibacterial property. Macrophage H-ferritin plays an important role in hepcidin-mediated protection against endotoxin-induced inflammation. We uncover a novel prophylactic and therapeutic role of hepcidin in sepsis-associated bacteremia, AKI, and mortality.

Potential of Food Hydrolyzed Proteins and Peptides to Chelate Iron or Calcium and Enhance their Absorption

Iron and calcium are two essential micronutrients that have strong effects on nutrition and human health because of their involvement in several biological and redox processes. Iron is responsible for electron and oxygen transport, cell respiration, and gene expression, whereas calcium is responsible for intracellular metabolism, muscle contraction, cardiac function, and cell proliferation. The bioavailability of these nutrients in the body is dependent on enhancers and inhibitors, some of which are found in consumed foods. Hydrolyzed proteins and peptides from food proteins can bind these essential minerals in the body and facilitate their absorption and bioavailability. The binding is also important because excess free iron will increase oxidative stress and the risks of developing chronic diseases. This paper provides an overview of the function of calcium and iron, and strategies to enhance their absorption with an emphasis on hydrolyzed proteins and peptides from foods. It also discusses the relationship between the structure of peptides and their potential to act as transition metal ligands.

Intersection of Iron and Copper Metabolism in the Mammalian Intestine and Liver

Iron and copper have similar physiochemical properties; thus, physiologically relevant interactions seem likely. Indeed, points of intersection between these two essential trace minerals have been recognized for many decades, but mechanistic details have been lacking. Investigations in recent years have revealed that copper may positively influence iron homeostasis, and also that iron may antagonize copper metabolism. For example, when body iron stores are low, copper is apparently redistributed to tissues important for regulating iron balance, including enterocytes of upper small bowel, the liver, and blood. Copper in enterocytes may positively influence iron transport, and hepatic copper may enhance biosynthesis of a circulating ferroxidase, ceruloplasmin, which potentiates iron release from stores. Moreover, many intestinal genes related to iron absorption are transactivated by a hypoxia-inducible transcription factor, hypoxia-inducible factor-2α (HIF2α), during iron deficiency. Interestingly, copper influences the DNA-binding activity of the HIF factors, thus further exemplifying how copper may modulate intestinal iron homeostasis. Copper may also alter the activity of the iron-regulatory hormone hepcidin. Furthermore, copper depletion has been noted in iron-loading disorders, such as hereditary hemochromatosis. Copper depletion may also be caused by high-dose iron supplementation, raising concerns particularly in pregnancy when iron supplementation is widely recommended. This review will cover the basic physiology of intestinal iron and copper absorption as well as the metabolism of these minerals in the liver. Also considered in detail will be current experimental work in this field, with a focus on molecular aspects of intestinal and hepatic iron-copper interplay and how this relates to various disease states. © 2018 American Physiological Society. Compr Physiol 8:1433-1461, 2018.

DNA methylation of hepatic iron sensing genes and the regulation of hepcidin expression

Production of the iron regulatory peptide hepcidin is tightly controlled by a network of proteins in hepatocytes that sense levels of iron in the circulation (as diferric-transferrin) and in tissues (in ferritin). Human studies show high variability in the normal range of serum hepcidin levels. We have postulated that this may, in part, be related to inter-individual variability in the expression of genes in the iron sensing pathway, potentially governed by epigenetic factors. Here, we have investigated whether genes encoding hepatic iron sensing proteins and hepcidin are regulated by DNA methylation. Experiments were performed on two human hepatoma cell lines, HepG2 cells and Huh7 cells. Basal expression of TFR2 and HAMP was significantly lower in Huh7 cells compared with HepG2 cells. Analysis of bisulphite-converted DNA from Huh7 cells revealed partial methylation of TFR2 (alpha transcript), which could result in gene silencing. Demethylation using 5-aza-2’-deoxycitidine (AZA) increased TFR2 mRNA expression in Huh7. PCR analysis of bisulphite-converted HAMP promoter DNA, using methylation-specific primers, revealed no differences between cell lines. However, HAMP mRNA expression in Huh7 was increased by AZA treatment, suggesting that methylation of one or more iron sensing genes may indirectly influence HAMP expression. Our study provides evidence that DNA methylation might control expression of HAMP and other hepatic iron sensing genes, and indicates that epigenetic influences on iron homeostasis warrant further investigation.

Quercetin inhibits intestinal non-haem iron absorption by regulating iron metabolism genes in the tissues

Purpose

There is general agreement that some dietary polyphenols block non-haem iron uptake, but the mechanisms by which they achieve this action are poorly understood. Since the polyphenol quercetin is ingested daily in significant amounts, we have investigated the effect of quercetin on duodenal non-haem iron absorption in vivo, as well as its effect on factors known to be involved in systemic iron metabolism.

Methods

Rats were subject to gastric gavage and systemic quercetin administration. Treatments were followed with uptake studies using radiolabeled iron, serum iron and transferrin saturation measurements, LC-MS/MS analysis of quercetin metabolites in serum, determination of tissue non-haem iron content and analysis of gene expression of iron-related proteins.

Results

Both oral and intraperitoneal (IP) quercetin caused serum and tissue iron depletion by two means, first by increasing mucosal iron uptake and inhibiting iron efflux from duodenal mucosa, and second by decreasing levels of duodenal DMT1, Dcytb and FPN. Additionally, IP quercetin induced highly significant increased liver expression of hepcidin, a hormone known to inhibit intestinal iron uptake.

Conclusions

Oral quercetin significantly inhibited iron absorption, while IP quercetin significantly affected iron-related genes. These results could lead to development of new effective ways of preventing and treating iron deficiency anaemia, the most widespread nutritional disorder in the world.

Electronic supplementary material

The online version of this article (10.1007/s00394-018-1680-7) contains supplementary material, which is available to authorized users.

The ferroportin-ceruloplasmin system and the mammalian iron homeostasis machine: regulatory pathways and the role of lactoferrin

In the last 20 years, several new genes and proteins involved in iron metabolism in eukaryotes, particularly related to pathological states both in animal models and in humans have been identified, and we are now starting to unveil at the molecular level the mechanisms of iron absorption, the regulation of iron transport and the homeostatic balancing processes. In this review, we will briefly outline the general scheme of iron metabolism in humans and then focus our attention on the cellular iron export system formed by the permease ferroportin and the ferroxidase ceruloplasmin. We will finally summarize data on the role of the iron binding protein lactoferrin on the regulation of the ferroportin/ceruloplasmin couple and of other proteins involved in iron homeostasis in inflamed human macrophages.

Disorders of Iron Metabolism and Anemia in Chronic Kidney Disease

Dysregulated iron homeostasis plays a central role in the development of anemia of chronic kidney disease (CKD) and is a major contributor toward resistance to treatment with erythropoiesis-stimulating agents. Understanding the underlying pathophysiology requires an in-depth understanding of normal iron physiology and regulation. Recent discoveries in the field of iron biology have greatly improved our understanding of the hormonal regulation of iron trafficking in human beings and how its alterations lead to the development of anemia of CKD. In addition, emerging evidence has suggested that iron homeostasis interacts with bone and mineral metabolism on multiple levels, opening up new avenues of investigation into the genesis of disordered iron metabolism in CKD. Building on recent advances in our understanding of normal iron physiology and abnormalities in iron homeostasis in CKD, this review characterizes how anemia related to disordered iron metabolism develops in the setting of CKD. In addition, this review explores our emerging recognition of the connections between iron homeostasis and mineral metabolism and their implications for the management of altered iron status and anemia of CKD.

Structure-function analysis of ferroportin defines the binding site and an alternative mechanism of action of hepcidin

Nonclassical ferroportin disease (FD) is a form of hereditary hemochromatosis caused by mutations in the iron transporter ferroportin (Fpn), resulting in parenchymal iron overload. Fpn is regulated by the hormone hepcidin, which induces Fpn endocytosis and cellular iron retention. We characterized 11 clinically relevant and 5 nonclinical Fpn mutations using stably transfected, inducible isogenic cell lines. All clinical mutants were functionally resistant to hepcidin as a consequence of either impaired hepcidin binding or impaired hepcidin-dependent ubiquitination despite intact hepcidin binding. Mapping the residues onto 2 computational models of the human Fpn structure indicated that (1) mutations that caused ubiquitination-resistance were positioned at helix-helix interfaces, likely preventing the hepcidin-induced conformational change, (2) hepcidin binding occurred within the central cavity of Fpn, (3) hepcidin interacted with up to 4 helices, and (4) hepcidin binding should occlude Fpn and interfere with iron export independently of endocytosis. We experimentally confirmed hepcidin-mediated occlusion of Fpn in the absence of endocytosis in multiple cellular systems: HEK293 cells expressing an endocytosis-defective Fpn mutant (K8R), Xenopus oocytes expressing wild-type or K8R Fpn, and mature human red blood cells. We conclude that nonclassical FD is caused by Fpn mutations that decrease hepcidin binding or hinder conformational changes required for ubiquitination and endocytosis of Fpn. The newly documented ability of hepcidin and its agonists to occlude iron transport may facilitate the development of broadly effective treatments for hereditary iron overload disorders.

New perspectives on the regulation of iron absorption via cellular zinc concentrations in humans

Iron deficiency is the most prevalent nutritional deficiency, affecting more than 30% of the total world's population. It is a major public health problem in many countries around the world. Over the years various methods have been used with an effort to try and control iron-deficiency anemia. However, there has only been a marginal reduction in the global prevalence of anemia. Why is this so? Iron and zinc are essential trace elements for humans. These metals influence the transport and absorption of one another across the enterocytes and hepatocytes, due to similar ionic properties. This paper describes the structure and roles of major iron and zinc transport proteins, clarifies iron-zinc interactions at these sites, and provides a model for the mechanism of these interactions both at the local and systemic level. This review provides evidence that much of the massive extent of iron deficiency anemia in the world may be due to an underlying deficiency of zinc. It explains the reasons for predominance of cellular zinc status in determination of iron/zinc interactions and for the first time thoroughly explains mechanisms by which zinc brings about these changes.

Hepcidin Attenuates Zinc Efflux in Caco-2 Cells

BACKGROUND

Hepcidin mediates the hypoferremia of inflammation by inhibiting iron transfer into circulation; however, a regulator for the hypozincemia observed in individuals with acute and chronic inflammatory and infectious diseases is not known.

OBJECTIVE

The objective of this study was to determine the effects of hepcidin on zinc transport in intestinal epithelial cells.

METHODS

Differentiated human intestinal Caco-2 cells were untreated or treated with 1 μM hepcidin for 3-24 h. Zinc transport was assessed in cells seeded on Transwell inserts. Media from the apical and basolateral chambers were collected, and zinc concentrations were determined using ⁶⁷Zn. Labile zinc pools were imaged and quantified in cells loaded with FluoZin-3-AM and expression of metallothionein and the zinc transporters zrt-/irt-like protein (ZIP)4 (SLC39A4), ZIP5 (SLC39A5), ZIP14 (SLC39A14), and zinc transporter 1 (ZnT1) (SLC30A1) was determined. Cells were transfected with SLC40A1- or SLC30A1-specific small interfering RNA to knock down ferroportin and ZnT1 protein, respectively. Cell surface proteins were isolated by cell surface biotinylation and lysosomal and proteasomal degradation was inhibited by treating cells with chloroquine or MG132, respectively.

RESULTS

Hepcidin attenuated zinc transport, as cells treated with hepcidin exported 26% less ⁶⁷Zn (P < 0.05) into the basolateral chamber and retained 27% more cellular ⁶⁷Zn (P < 0.05) than did control cells. Labile zinc decreased, and the mRNA abundance of metallothionein increased by ∼50% in hepcidin-treated cells compared with control cells (P < 0.05). Hepcidin reduced ZnT1 protein by 75% (P < 0.05) compared with control cells. Hepcidin-mediated reductions in zinc export remained in ferroportin knockdown cells compared with untreated controls (P < 0.05), whereas knockdown of ZnT1 inhibited this effect (P ≥ 0.05). Hepcidin significantly reduced biotinylated cell surface ZnT1 compared with control cells (P < 0.05); chloroquine inhibited hepcidin-mediated degradation of ZnT1 (P ≥ 0.05), whereas MG132 had no effect (P < 0.05).

CONCLUSIONS

Hepcidin reduces intestinal zinc export by post-translationally downregulating ZnT1 through a lysosomal-mediated degradation pathway, indicating that hepcidin may contribute to the hypozincemia of inflammation and infection.

Ironing out Ferroportin

Maintaining physiologic iron concentrations in tissues is critical for metabolism and host defense. Iron absorption in the duodenum, recycling of iron from senescent erythrocytes, and iron mobilization from storage in macrophages and hepatocytes constitute the major iron flows into plasma for distribution to tissues, predominantly for erythropoiesis. All iron transfer to plasma occurs through the iron exporter ferroportin. The concentration of functional membrane-associated ferroportin is controlled by its ligand, the iron-regulatory hormone hepcidin, and fine-tuned by regulatory mechanisms serving iron homeostasis, oxygen utilization, host defense, and erythropoiesis. Fundamental questions about the structure and biology of ferroportin remain to be answered.

Age-dependent expression of duodenal cytochrome b, divalent metal transporter 1, ferroportin 1, and hephaestin in the duodenum of rats

BACKGROUND AND AIM

The body's requirement for iron is different at different developmental stages. However, the molecular mechanisms of age-dependent iron metabolism are poorly understood. In the present study, we investigated the expression of iron transport proteins in the duodenum of Sprague-Dawley rats at five different age stages.

METHODS

Male Sprague-Dawley rats at postnatal week (PNW) 1, 3, 12, 44, and 88 were employed in the study. Serum iron status and tissue non-heme iron concentrations in the spleen, liver, bone marrow, heart, kidney, duodenal epithelium, and gastrocnemius were examined at each age stage. The expression of duodenal cytochrome b (DcytB), divalent metal transporter 1 (DMT1), ferroportin 1 (FPN1), hephaestin, and hepcidin were measured by real-time polymerase chain reaction or Western blot.

RESULTS

The levels of serum iron and transferrin saturation were higher in the rats at PNW1 and 3 than in those at PNW12, 44, and 88. Non-heme iron contents decreased from PNW1 to PNW3 and then increased thereafter. Duodenal DcytB, DMT1, and FPN1 increased to the highest level at PNW3 and then decreased from PNW12 to 88. The hepatic hepcidin mRNA level decreased to the lowest level at PNW3 and then increased with age.

CONCLUSION

Our findings showed that age had a significant effect on body iron status. The increased duodenal DcytB, DMT1, and FPN1 expression can enhance intestinal iron absorption to meet the high iron requirements in infants. Hepcidin or enterocyte iron levels may be involved in the regulation of age-dependent FPN1, DMT1, and DcytB expression in the duodenum.

Duodenal absorption and tissue utilization of dietary heme and nonheme iron differ in rats

BACKGROUND

Dietary heme contributes to iron intake, yet regulation of heme absorption and tissue utilization of absorbed heme remains undefined.

OBJECTIVES

In a rat model of iron overload, we used stable iron isotopes to examine heme- and nonheme-iron absorption in relation to liver hepcidin and to compare relative utilization of absorbed heme and nonheme iron by erythroid (RBC) and iron storage tissues (liver and spleen).

METHODS

Twelve male Sprague-Dawley rats were randomly assigned to groups for injections of either saline or iron dextran (16 or 48 mg Fe over 2 wk). After iron loading, rats were administered oral stable iron in the forms of (57)Fe-ferrous sulfate and (58)Fe-labeled hemoglobin. Expression of liver hepcidin and duodenal iron transporters and tissue stable iron enrichment was determined 10 d postdosing.

RESULTS

High iron loading increased hepatic hepcidin by 3-fold and reduced duodenal expression of divalent metal transporter 1 (DMT1) by 76%. Nonheme-iron absorption was 2.5 times higher than heme-iron absorption (P = 0.0008). Absorption of both forms of iron was inversely correlated with hepatic hepcidin expression (heme-iron absorption: r = -0.77, P = 0.003; nonheme-iron absorption: r = -0.80, P = 0.002), but hepcidin had a stronger impact on nonheme-iron absorption (P = 0.04). Significantly more (57)Fe was recovered in RBCs (P = 0.02), and more (58)Fe was recovered in the spleen (P = 0.01).

CONCLUSIONS

Elevated hepcidin significantly decreased heme- and nonheme-iron absorption but had a greater impact on nonheme-iron absorption. Differential tissue utilization of heme vs. nonheme iron was evident between erythroid and iron storage tissues, suggesting that some heme may be exported into the circulation in a form different from that of nonheme iron.

Iron in Eukarya

Iron is essential for the normal physiological function of all organisms. In humans it is required for a plethora of biochemical roles including the transport of oxygen in the blood and energy production in the mitochondria. However, iron is also highly cytotoxic when present at high levels as it readily participates in oxidation-reduction reactions that lead to the generation of reactive oxygen species. One unique feature of iron biology is the lack of excretory mechanisms to remove excess iron from the body. Therefore, the concerted action of several genes and proteins working together to regulate the movement of iron across cell membranes, its storage in peripheral tissues and its physiological utilization in the body is essential for maintaining iron homeostasis. Humans are exposed to iron in a number of chemical forms (haem or non-haem; ferric or ferrous). This chapter will describe how humans acquire iron from their diet; the subsequent delivery of iron to its sites of utilization and storage; and how iron is recycled from effete erythrocytes for re-use in metabolism. Mutations in a number of the genes controlling iron metabolism have been identified and study of the pathological consequences of these mutations has allowed us to gain a greater understanding of how the body senses changes in iron status and coordinates its transport, storage and utilization to maintain homeostasis.

The IRP/IRE system in vivo: insights from mouse models

Iron regulatory proteins 1 and 2 (IRP1 and IRP2) post-transcriptionally control the expression of several mRNAs encoding proteins of iron, oxygen and energy metabolism. The mechanism involves their binding to iron responsive elements (IREs) in the untranslated regions of target mRNAs, thereby controlling mRNA translation or stability. Whereas IRP2 functions solely as an RNA-binding protein, IRP1 operates as either an RNA-binding protein or a cytosolic aconitase. Early experiments in cultured cells established a crucial role of IRPs in regulation of cellular iron metabolism. More recently, studies in mouse models with global or localized Irp1 and/or Irp2 deficiencies uncovered new physiological functions of IRPs in the context of systemic iron homeostasis. Thus, IRP1 emerged as a key regulator of erythropoiesis and iron absorption by controlling hypoxia inducible factor 2α (HIF2α) mRNA translation, while IRP2 appears to dominate the control of iron uptake and heme biosynthesis in erythroid progenitor cells by regulating the expression of transferrin receptor 1 (TfR1) and 5-aminolevulinic acid synthase 2 (ALAS2) mRNAs, respectively. Targeted disruption of either Irp1 or Irp2 in mice is associated with distinct phenotypic abnormalities. Thus, Irp1(-/-) mice develop polycythemia and pulmonary hypertension, while Irp2(-/-) mice present with microcytic anemia, iron overload in the intestine and the liver, and neurologic defects. Combined disruption of both Irp1 and Irp2 is incombatible with life and leads to early embryonic lethality. Mice with intestinal- or liver-specific disruption of both Irps are viable at birth but die later on due to malabsorption or liver failure, respectively. Adult mice lacking both Irps in the intestine exhibit a profound defect in dietary iron absorption due to a "mucosal block" that is caused by the de-repression of ferritin mRNA translation. Herein, we discuss the physiological function of the IRE/IRP regulatory system.

Quercetin inhibits intestinal iron absorption and ferroportin transporter expression in vivo and in vitro

Balancing systemic iron levels within narrow limits is critical for maintaining human health. There are no known pathways to eliminate excess iron from the body and therefore iron homeostasis is maintained by modifying dietary absorption so that it matches daily obligatory losses. Several dietary factors can modify iron absorption. Polyphenols are plentiful in human diet and many compounds, including quercetin--the most abundant dietary polyphenol--are potent iron chelators. The aim of this study was to investigate the acute and longer-term effects of quercetin on intestinal iron metabolism. Acute exposure of rat duodenal mucosa to quercetin increased apical iron uptake but decreased subsequent basolateral iron efflux into the circulation. Quercetin binds iron between its 3-hydroxyl and 4-carbonyl groups and methylation of the 3-hydroxyl group negated both the increase in apical uptake and the inhibition of basolateral iron release, suggesting that the acute effects of quercetin on iron transport were due to iron chelation. In longer-term studies, rats were administered quercetin by a single gavage and iron transporter expression measured 18 h later. Duodenal FPN expression was decreased in quercetin-treated rats. This effect was recapitulated in Caco-2 cells exposed to quercetin for 18 h. Reporter assays in Caco-2 cells indicated that repression of FPN by quercetin was not a transcriptional event but might be mediated by miRNA interaction with the FPN 3'UTR. Our study highlights a novel mechanism for the regulation of iron bioavailability by dietary polyphenols. Potentially, diets rich in polyphenols might be beneficial for patients groups at risk of iron loading by limiting the rate of intestinal iron absorption.

Effects of acute dietary iron overload in pigs (Sus scrofa) with induced type 2 diabetes mellitus

Epidemiological studies have reported an association between high iron (Fe) levels and elevated risk of developing type 2 diabetes mellitus (T2D). It is believed that the formation of Fe-catalyzed hydroxyl radicals may contribute to the development of diabetes. Our goal was to determine the effect of a diet with a high Fe content on type 2 diabetic pigs. Four groups of piglets were studied: (1) control group, basal diet; (2) Fe group, basal diet with 3,000 ppm ferrous sulfate; (3) diabetic group (streptozotocin-induced type 2 diabetes) with basal diet; (4) diabetic/Fe group, diabetic animals/3,000 ppm ferrous sulfate. For 2 months, biochemical and hematological parameters were evaluated. Tissue samples of liver and duodenum were obtained to determine mRNA relative abundance of DMT1, ferroportin (Fpn), ferritin (Fn), hepcidin (Hpc), and transferrin receptor by qRT-PCR. Fe group presented increased levels of hematological (erythrocytes, hematocrit, and hemoglobin) and iron parameters. Diabetic/Fe group showed similar behavior as Fe group but in lesser extent. The relative abundance of different genes in the four study groups yielded a different expression pattern. DMT1 showed a lower expression in the two iron groups compared with control and diabetic animals, and Hpc showed an increased on its expression in Fe and diabetic/Fe groups. Diabetic/Fe group presents greater expression of Fn and Fpn. These results suggest that there is an interaction between Fe nutrition, inflammation, and oxidative stress in the diabetes development.

Hepcidin and sports anemia

Iron is an important mineral element used by the body in a variety of metabolic and physiologic processes. These processes are highly active when the body is undergoing physical exercises. Prevalence of exercise-induced iron deficiency anemia (also known as sports anemia) is notably high in athletic populations, particularly those with heavy training loads. The pathogenesis of sports anemia is closely related to disorders of iron metabolism, and a more comprehensive understanding of the mechanism of iron metabolism in the course of physical exercises could expand ways of treatment and prevention of sports anemia. In recent years, there have been remarkable research advances regarding the molecular mechanisms underlying changes of iron metabolism in response to physical exercises. This review has covered these advances, including effects of exercise on duodenum iron absorption, serum iron status, iron distribution in organs, erythropoiesis, and hepcidin’s function and its regulation. New methods for the treatment of exercise-induced iron deficiency are also discussed.

Proposing a Caco-2/HepG2 cell model for in vitro iron absorption studies

The Caco-2 cell line is well established as an in vitro model for iron absorption. However, the model does not reflect the regulation of iron absorption by hepcidin produced in the liver. We aimed to develop the Caco-2 model by introducing human liver cells (HepG2) to Caco-2 cells. The Caco-2 and HepG2 epithelia were separated by a liquid compartment, which allowed for epithelial interaction. Ferritin levels in cocultured Caco-2 controls were 21.7±10.3 ng/mg protein compared to 7.7±5.8 ng/mg protein in monocultured Caco-2 cells. The iron transport across Caco-2 layers was increased when liver cells were present (8.1%±1.5% compared to 3.5%±2.5% at 120 μM Fe). Caco-2 cells were exposed to 0, 80 and 120 μM Fe and responded with increased hepcidin production at 120 μM Fe (3.6±0.3 ng/ml compared to 2.7±0.3 ng/ml). The expression of iron exporter ferroportin in Caco-2 cells was decreased at the hepcidin concentration of 3.6 ng/ml and undetectable at external addition of hepcidin (10 ng/ml). The apical transporter DMT1 was also undetectable at 10 ng/ml but was unchanged at the lower concentrations. In addition, we observed that sourdough bread, in comparison to heat-treated bread, increased the bioavailability of iron despite similar iron content (53% increase in ferritin formation, 97% increase in hepcidin release). This effect was not observed in monocultured Caco-2 cells. The Caco-2/HepG2 model provides an alternative approach to in vitro iron absorption studies in which the hepatic regulation of iron transport must be considered.

Iron overload induces changes of pancreatic and duodenal divalent metal transporter 1 and prohepcidin expression in mice

It is well known that the iron content of the body is tightly regulated. Iron excess induces adaptive changes that are differentially regulated in each tissue. The pancreas is particularly susceptible to iron-related disorders. We studied the expression and regulation of key iron proteins in the pancreas, duodenum and liver, using an animal model of iron overload (female CF1 mice injected i.p. with iron saccharate, colloidal iron form). Divalent metal transporter 1, prohepcidin and ferritin (pancreas, duodenum, liver) were assessed by immunohistochemistry; divalent metal transporter 1 (pancreas, duodenum) by Western blot. In the iron overloaded mice, prohepcidin expression increased in islets of Langerhans and hepatocytes, and divalent metal transporter 1 expression decreased in cells of islets and in enterocytes. In the iron overloaded mice, ferritin expression decreased in islets of Langerhans and increased in acinar cells; hemosiderin was localized in connective tissue cells. The inverse relationship between divalent metal transporter 1 and prohepcidin may indicate a negative regulation by hepcidin, and hence reduction of iron stores in islets of Langerhans. Our data showed that in iron overloaded mice model, induced by colloidal iron form, a coordinated expression of key iron proteins in the pancreas, duodenum and liver may occur. Further research will be necessary to determine the adaptive responses induced by iron in the pancreas.

Responsiveness to parenteral iron therapy in children with oral iron-refractory iron-deficiency anemia

Intravenous (IV) ferric iron (Fe)-carbohydrate complexes are used for treating Fe deficiency in children with iron-refractory iron-deficiency anemia (IRIDA). An optimal treatment has yet to be determined. There are relatively little publications on the responsiveness to IV iron therapy in children with IRIDA.

PATIENTS AND METHOD

This study analyzed responses to IV iron sucrose therapy given to 11 children, ranging in age from 2 to 13 years (mean 4.8 years), with iron-deficiency anemia who were unresponsive to oral iron therapy.

RESULTS

The hemoglobin and ferritin values (mean) of the 11 children with IRIDA were 7.7 g/dL and 4.8 ng/mL at diagnosis. Both hemoglobin and ferritin levels increased to 9.5 g/dL, and 24 ng/mL, respectively, at 6 weeks after the first therapy. Although the level of hemoglobin was steady at 6 months after the first, and 6 weeks after the second therapy, the ferritin levels continued to increase up to 30 ng/mL and 47 ng/mL at 6 months after the first and 6 weeks after the second therapy, respectively.

CONCLUSION

We recommend that IRIDA should be considered in patients presenting with iron-deficiency anemia of unknown cause that is unresponsive to oral iron therapy. Our results suggest that IV iron therapy should be administered only once in cases of IRIDA. Continued administration of IV iron would be of no benefit to increase hemoglobin levels. On the contrary, ferritin levels may continue to increase resulting in untoward effects of hyperferritinemia.

Epidemiological and nonclinical studies investigating effects of iron in carcinogenesis--a critical review

The efficacy and tolerability of intravenous (i.v.) iron in managing cancer-related anemia and iron deficiency has been clinically evaluated and reviewed recently. However, long-term data in cancer patients are not available; yet, long-term i.v. iron treatment in hemodialysis patients is not associated with increased cancer risk. This review summarizes epidemiological and nonclinical data on the role of iron in carcinogenesis. In humans, epidemiological data suggest correlations between certain cancers and increased iron exposure or iron overload. Nonclinical models that investigated whether iron can enhance carcinogenesis provide only limited evidence relevant for cancer patients since they were typically based on high iron doses as well as injection routes and iron formulations which are not used in the clinical setting. Nevertheless, in the absence of long-term outcome data from prospectively defined trials in i.v. iron-treated cancer patients, iron supplementation should be limited to periods of concomitant anti-tumor treatment.

Ferroportin and exocytoplasmic ferroxidase activity are required for brain microvascular endothelial cell iron efflux

The mechanism(s) of iron flux across the brain microvasculature endothelial cells (BMVEC) of the blood-brain barrier remains unknown. Although both hephaestin (Hp) and the ferrous iron permease ferroportin (Fpn) have been identified in BMVEC, their roles in iron efflux have not been examined. Using a human BMVEC line (hBMVEC), we have demonstrated that these proteins are required for iron efflux from these cells. Expression of both Hp and Fpn protein was confirmed in hBMVEC by immunoblot and indirect immunofluorescence; we show that hBMVEC express soluble ceruloplasmin (Cp) transcript as well. Depletion of endogenous Hp and Cp via copper chelation leads to the reduction of hBMVEC Fpn protein levels as well as a complete inhibition of (59)Fe efflux. Both hBMVEC Fpn protein and (59)Fe efflux activity are restored upon incubation with 6.6 nm soluble plasma Cp. These results are independent of the source of cell iron, whether delivered as transferrin- or non-transferrin-bound (59)Fe. Our results demonstrate that iron efflux from hBMVEC Fpn requires the action of an exocytoplasmic ferroxidase, which can be either endogenous Hp or extracellular Cp.

Effects of elevated dietary iron on the gastrointestinal expression of Nramp genes and iron homeostasis in rainbow trout (Oncorhynchus mykiss)

Diet is the primary source of iron (Fe) for freshwater fish, and the absorption of Fe is believed to occur via the Nramp family of divalent metal transporters (also called DMT1). Presently, the homeostatic regulation of dietary Fe absorption in fish is poorly understood. This study examined the gastrointestinal mRNA expression of two Nramp isoforms, Nramp-β and Nramp-γ, in the freshwater rainbow trout (Oncorhynchus mykiss), following exposure to elevated dietary Fe [1,256 mg Fe/kg food vs. 136 mg Fe/kg food (control)] for 14 days. The physiological performance, plasma Fe status and tissue-specific accumulation of Fe were also evaluated. In general, the mRNA expression level of Nramp was higher in the intestine relative to the stomach. Interestingly, fish fed on a high-Fe diet exhibited a significant induction in Nramp expression after 7 days, followed by a decrease to the level observed in control fish on day 14. The increase in Nramp expression correlated with the elevated gastrointestinal and plasma Fe concentrations. However, the hepatic Fe concentration remained unchanged during the entire exposure period, indicating strong homeostatic regulation of hepatic Fe level in fish. Fish appeared to handle increased systemic Fe level by elevating the plasma transferrin level, thereby enhancing the Fe-binding capacity in the plasma. Overall, our study provides new interesting insights into the homeostatic regulation of dietary Fe uptake and handling in freshwater fish.

Copper deficiency leads to anemia, duodenal hypoxia, upregulation of HIF-2α and altered expression of iron absorption genes in mice

Iron and copper are essential trace metals, actively absorbed from the proximal gut in a regulated fashion. Depletion of either metal can lead to anemia. In the gut, copper deficiency can affect iron absorption through modulating the activity of hephaestin - a multi-copper oxidase required for optimal iron export from enterocytes. How systemic copper status regulates iron absorption is unknown. Mice were subjected to a nutritional copper deficiency-induced anemia regime from birth and injected with copper sulphate intraperitoneally to correct the anemia. Copper deficiency resulted in anemia, increased duodenal hypoxia and Hypoxia inducible factor 2α (HIF-2α) levels, a regulator of iron absorption. HIF-2α upregulation in copper deficiency appeared to be independent of duodenal iron or copper levels and correlated with the expression of iron transporters (Ferroportin - Fpn, Divalent Metal transporter - Dmt1) and ferric reductase - Dcytb. Alleviation of copper-dependent anemia with intraperitoneal copper injection resulted in down regulation of HIF-2α-regulated iron absorption genes in the gut. Our work identifies HIF-2α as an important regulator of iron transport machinery in copper deficiency.

Physiological focus on the erythropoietin-hepcidin-ferroportin axis

To analyze the interconnection between erythropoiesis and iron metabolism, one of the issues raised in this study was to know iron bioavailability under physiopathological conditions. Our aim was to understand the functional axis response composed of erythropoietin (Epo)-hepcidin-ferroportin (FPN), when 2 dysfunctional states coexist, using an animal model of iron overload followed by hypoxia. FPN and prohepcidin were assessed by immunohistochemistry using rabbit anti-mouse FPN polyclonal and prohepcidin monoclonal antibodies. Goat-labeled polymer - horseradish peroxidase anti-rabbit EnVision + System (DAB) was used as the secondary antibody. Epo levels were measured by ELISA. Tissue iron was studied by Prussian blue iron staining. Erythropoietic response was assessed using conventional hematological tests. Iron overload increased prohepcidin that remained high in hypoxia, coexisting with high levels of Epo in hypoxia, with or without iron overload. In hypoxia, FPN was clearly evident in reticuloendothelial macrophages, more than in hypoxia with iron overload. Interestingly, duodenal FPN was clearly identified on the basolateral membrane in hypoxia, with or without iron overload. Our data indicate that 2 signals could induce the cell-specific response as follows: (i) iron signal, induced prohepcidin, which reduced reticuloendothelial FPN and reduced iron availability; and (ii) hypoxia signal, stimulated Epo, which affected iron absorption by stabilizing duodenal FPN and allowed iron supply to erythropoiesis independently of store size.

Heme Iron Intake and Risk of Stroke

Background and Purpose—

Intake of iron, especially heme iron, has been associated with several diseases. However, epidemiological studies of heme iron and nonheme iron intake in relation to risk of stroke are lacking. The aim of this study was to examine the associations between heme iron and nonheme iron intake and stroke incidence in men.

Methods—

The population-based prospective Cohort of Swedish Men included 38 859 men, aged 45 to 79 years, who had no history of stroke, coronary heart disease, or cancer at baseline. Hazard ratios and 95% confidence intervals (95% CIs) were calculated using Cox proportional hazards regression models.

Results—

During an 11.7 years follow-up, 3097 incident cases of stroke, including 2482 cerebral infarctions and 450 intracerebral hemorrhages, were registered. The hazard ratios of total stroke and cerebral infarction for the highest compared with the lowest quintiles of heme iron intake were 1.16 (95% CI, 1.03–1.31; P trend=0.037) and 1.15 (95% CI, 1.00–1.31; P trend=0.089), respectively. The incidence rates of total stroke per 10 000 person-years were 72.6 in the lowest quintile and 84.4 in the highest. The association was confined to men with body mass index <25 kg/m 2 , the hazard ratios were 1.40 (95% CI, 1.17–1.68; P trend<0.001) for total stroke and 1.38 (95% CI, 1.13–1.70; P trend=0.001) for cerebral infarction; no association was observed among overweight and obese men. There was no association between nonheme iron intake and risk of total stroke and stroke types.

Conclusions—

Findings from this prospective study indicate that a high heme iron intake, particularly in normal weight individuals, may increase the risk of stroke.

Iron refractory iron deficiency anemia: presentation with hyperferritinemia and response to oral iron therapy

Iron-refractory iron-deficiency anemia (IRIDA) is an autosomal recessive disorder caused by mutations in TMPRSS6. Patients have hypochromic microcytic anemia refractory to oral iron and are only partially responsive to parenteral iron administration. We report a French-Canadian kindred in which 2 siblings presented in early childhood with severe microcytic anemia, hypoferremia, and hyperferritinemia. Both children have been successfully treated solely with low-dose oral iron since diagnosis. Clinical and biological presentation did not fit any previously described genetic iron-deficiency anemia. Whole exome sequencing identified in both patients compound heterozygous mutations of TMPRSS6 leading to p.G442R and p.E522K, 2 mutations previously reported to cause classic IRIDA, and no additional mutations in known iron-regulatory genes. Thus, the phenotype associated with the unique combination of mutations uncovered in both patients expands the spectrum of disease associated with TMPRSS6 mutations to include iron deficiency anemia that is accompanied by hyperferritinemia at initial presentation and is responsive to continued oral iron therapy. Our results have implications for genetic testing in early childhood iron deficiency anemia. Importantly, they emphasize that whole exome sequencing can be used as a diagnostic tool and greatly facilitate the elucidation of the genetic basis of unusual clinical presentations, including hypomorphic mutations or compound heterozygosity leading to different phenotypes in known Mendelian diseases.

Effect of ferroportin polymorphism on iron homeostasis and infection

Ferroportin (FPN) is the sole iron export membrane protein identified in mammals that is abundantly expressed on absorptive enterocytes and macrophages, and is essential for physiological regulation of cellular iron. The expression of FPN is positively induced by cellular iron and is suppressed by liver hepcidin in response to either increased systemic iron or inflammatory stimuli. Hepcidin binds to cell surface FPN inducing FPN internalization followed by lysosomal degradation of the protein and consequently iron efflux from macrophages is blocked and there is suboptimal iron absorption by duodenal enterocytes. Dozens of FPN gene mutations have been identified in different ethnic populations and some of the mutations are associated with autosomal dominant iron overload disorder described as FPN disease or hemochromatosis type 4 that is distinct from hereditary hemochromatosis due to HFE mutations. Clinical manifestations of iron overload FPN disease can be classified into two groups according to whether there is selective macrophage iron loading or parenchymal and reticuloendothelial iron accumulation. There is evidence suggesting that altered hepcidin-FPN interaction can modulate host's response to infection. Resistance to hepcidin promotes iron egress from cells and this inhibits growth of intracellular pathogens. Conversely, iron retention due to loss of iron export activity by mutated FPN results in intracellular iron accumulation and a permissive environment for intracellular pathogens.

Tumour necrosis factor alpha downregulates human hemojuvelin expression via a novel response element within its promoter

Background

Iron homeostasis is chiefly regulated by hepcidin whose expression is tightly controlled by inflammation, iron stores, and hypoxia. Hemojuvelin (HJV) is a bone morphogenetic protein co-receptor that has been identified as a main upstream regulator of hepcidin expression; HJV mutations are associated with a severe form of iron overload (Juvenile haemochromatosis). Currently however, there is no information on how HJV is regulated by inflammation.

Methods

To study the regulation of Hjv expression by inflammation and whether Hfe has a role in that regulation, control and LPS-injected wild type and Hfe KO mice were used. Moreover, human hepatoma cells (HuH7) were used to study the effect of IL-6 and TNF-α on HJV mRNA expression.

Results

Here we show that LPS repressed hepatic Hjv and BMPs, while it induced hepcidin 1 expression in wild-type and Hfe KO mice with no effect on hepatic pSMAD 1, 5, 8 protein levels. In addition, exogenous TNF-α (20 ng/mL) decreased HJV mRNA and protein expression to 40% of control with no effect on hepcidin mRNA expression in 24 hours. On the other hand, IL-6 induced hepcidin mRNA and protein expression with no effect on HJV mRNA expression levels. Moreover, using the HJV promoter-luciferase reporter fusion construct (HJVP1.2-luc), we showed that the basal luciferase activity of HJVP1.2-luc was inhibited by 33% following TNF-α treatment of HuH7 transfected cells suggesting that the TNF-α down-regulation is exerted at the transcriptional level. Additionally, mutation of a canonical TNF- alpha responsive element (TNFRE) within HJVP1.2-luc abolished TNF-α response suggesting that this TNFRE is functional.

Conclusions

From these results, we conclude that TNF-α suppresses HJV transcription possibly via a novel TNFRE within the HJV promoter. In addition, the results suggest that the proposed link between inflammation and BMP-SMAD signalling is independent of HJV and BMP ligands.

Minihepcidins prevent iron overload in a hepcidin-deficient mouse model of severe hemochromatosis

The deficiency of hepcidin, the hormone that controls iron absorption and its tissue distribution, is the cause of iron overload in nearly all forms of hereditary hemochromatosis and in untransfused iron-loading anemias. In a recent study, we reported the development of minihepcidins, small drug-like hepcidin agonists. Here we explore the feasibility of using minihepcidins for the prevention and treatment of iron overload in hepcidin-deficient mice. An optimized minihepcidin (PR65) was developed that had superior potency and duration of action compared with natural hepcidin or other minihepcidins, and favorable cost of synthesis. PR65 was administered by subcutaneous injection daily for 2 weeks to iron-depleted or iron-loaded hepcidin knockout mice. PR65 administration to iron-depleted mice prevented liver iron loading, decreased heart iron levels, and caused the expected iron retention in the spleen and duodenum. At high doses, PR65 treatment also caused anemia because of profound iron restriction. PR65 administration to hepcidin knockout mice with pre-existing iron overload had a more moderate effect and caused partial redistribution of iron from the liver to the spleen. Our study demonstrates that minihepcidins could be beneficial in iron overload disorders either used alone for prevention or possibly as adjunctive therapy with phlebotomy or chelation.

Ferroportin-mediated iron transport: expression and regulation

The distinguishing feature between iron homeostasis in single versus multicellular organisms is the need for multicellular organisms to transfer iron from sites of absorption to sites of utilization and storage. Ferroportin is the only known iron exporter and ferroportin plays an essential role in the export of iron from cells to blood. Ferroportin can be regulated at many different levels including transcriptionally, post-transcriptionally, through mRNA stability and post-translationally, through protein turnover. Additionally, ferroportin may be regulated in both cell-dependent and cell-autonomous fashions. Regulation of ferroportin is critical for iron homeostasis as alterations in ferroportin may result in either iron deficiency or iron overload. This article is part of a Special Issue entitled: Cell Biology of Metals.

Hepcidin treatment modulates the expression of divalent metal transporter-1, ceruloplasmin, and ferroportin-1 in the rat cerebral cortex and hippocampus

Elevated iron levels are considered to play a role in the neurodegenerative mechanisms that underlie Alzheimer's and Parkinson's disease. The linkage between hepcidin (Hepc) and ferroportin-1 (FPN1), the divalent metal transporter 1 (DMT1), and ceruloplasmin (CP) in the brain is unknown. To discern the role of Hepc in regulating the expression of these proteins, we investigated FPN1, DMT1, and CP protein and mRNA expression in the brain after the intracerebroventricular injection of Hepc. Our results show that after Hepc injection, expression of FPN1 mRNA and FPN1 protein was inhibited in the cerebral cortex and hippocampus. Furthermore, we showed a clear change of DMT1 and CP protein and mRNA levels in the brain. The immunohistochemical analysis revealed an increase of DMT1 and a decrease of CP levels. Semi-quantitative analysis using PCR methods showed an increase of DMT1(+IRE) mRNA, and a decrease of DMT1(-IRE) mRNA and CP mRNA levels. Since alterations in iron levels in the brain are causally linked to degenerative conditions such as Alzheimer's disease, an improved understanding of the regulation of iron transport protein expression such as FPN1, DMT1, and CP could lead to novel strategies for treatments.

Intestinal DMT1 cotransporter is down-regulated by hepcidin via proteasome internalization and degradation

BACKGROUNDS & AIMS

The mechanism by which hepcidin regulates iron export from macrophages has been well established and is believed to involve degradation of ferroportin. However, in the small intestine, hepcidin's mechanisms of action are not known. We studied human polarized intestinal (Caco-2/TC7) cells and mouse duodenal segments, ex vivo, to investigate the molecular mechanisms by which hepcidin down-regulates intestinal transepithelial iron transport.

METHODS

Iron transport was analyzed using ⁵⁵FeNTA. Expression of Divalent Metal Transporter 1 (DMT1) and ferroportin was evaluated by reverse-transcription quantitative polymerase chain reaction and immunoblotting. Videomicroscopy analysis was performed on live cells that expressed either DMT1 or ferroportin fused to green fluorescent protein.

RESULTS

In Caco-2/TC7 cells, physiologic doses of hepcidin (50-1000 nmol/L) inhibited transport of ⁵⁵Fe in a dose-dependent manner; a half-maximum effect was observed at 75-100 nmol/L. However, 200 nmol/L hepcidin induced a significant decrease in DMT1 protein expression but no change in ferroportin protein levels, unlike macrophages. This result was confirmed ex vivo in isolated duodenal segments: 200 nmol/L hepcidin induced a significant reduction in iron transport and DMT1 protein levels but no change in ferroportin levels. In Caco-2/TC7 cells, the effect of hepcidin on the DMT1 protein level was completely abolished in the presence of a proteasome inhibitor (MG-132); DMT1 ubiquitination was induced by the addition of hepcidin.

CONCLUSIONS

An acute increase in hepcidin concentration reduces intestinal iron absorption through ubiquitin-dependent proteasome degradation of DMT1.

Iron, meat and health

This article is a summary of the publication "Iron and Health" by the Scientific Advisory Committee on Nutrition (SACN) to the U.K. Government (2010), which reviews the dietary intake of iron and the impact of different dietary patterns on the nutritional and health status of the U.K. population. It concludes that several uncertainties make it difficult to determine dose-response relationships or to confidently characterize the risks associated with iron deficiency or excess. The publication makes several recommendations concerning iron intakes from food, including meat, and from supplements, as well as recommendations for further research.

Iron absorption in hepcidin1 knockout mice

Hepcidin, the Fe-regulatory peptide, has been shown to inhibit Fe absorption and reticuloendothelial Fe recycling. The present study was conducted to explore the mechanism of in vivo Fe regulation through genetic disruption of hepcidin1 and acute effects of hepcidin treatment in hepcidin1 knockout (Hepc1-/-) and heterozygous mice. Hepcidin1 disruption resulted in significantly increased intestinal Fe uptake. Hepcidin injection inhibited Fe absorption in both genotypes, but the effects were more evident in the knockout mice. Hepcidin administration was also associated with decreased membrane localisation of ferroportin in the duodenum, liver and, most significantly, in the spleen of Hepc1-/- mice. Hypoferraemia was induced in heterozygous mice by hepcidin treatment, but not in Hepc1-/- mice, 4 h after injection. Interestingly, Fe absorption and serum Fe levels in Hepc1-/- and heterozygous mice fed a low-Fe diet were not affected by hepcidin injection. The present study demonstrates that hepcidin deficiency causes increased Fe absorption. The effects of hepcidin were abolished by dietary Fe deficiency, indicating that the response to hepcidin may be influenced by dietary Fe level or Fe status.

Hypoxia inhibits hepcidin expression in HuH7 hepatoma cells via decreased SMAD4 signaling

Hepcidin negatively regulates systemic iron homeostasis in response to inflammation and elevated serum iron. Conversely, hepcidin expression is diminished in response to hypoxia, oxidative stress, and increased erythropoietic demand, though the molecular intermediates involved are incompletely understood. To address this, we have investigated hypoxic hepcidin regulation in HuH7 hepatoma cells either cultured alone or cocultured with activated THP-1 macrophages. HuH7 hepcidin mRNA expression was determined using quantitative polymerase chain reaction (Q-PCR). Hepcidin promoter activity was measured using luciferase reporter constructs containing a 0.9 kb fragment of the wild-type human hepcidin promoter, and constructs containing mutations in bone morphogenetic protein (BMP)/SMAD4, signal transducer and activator of transcription 3 (STAT3), CCAAT/enhancer-binding protein (C/EBP), and E-box-responsive elements. Hepatic expression of bone morphogenetic proteins BMP2 and BMP6 and the BMP inhibitor noggin was determined using Q-PCR, and the protein expression of hemojuvelin (HJV), pSMAD 1/5/8, and SMAD4 was determined by western blotting. Following exposure to hypoxia or H(2)O(2), hepcidin mRNA expression and promoter activity increased in HuH7 cells monocultures but were decreased in HuH7 cells cocultured with THP-1 macrophages. This repression was attenuated by mutation of the BMP/SMAD4-response element, suggesting that modulation of SMAD signaling mediated the response to hypoxia. No changes in hepatocyte BMP2, BMP6 or noggin mRNA, or protein expression of HJV or pSMAD 1/5/8 were detected. However, treatment with hypoxia caused a marked decrease in nuclear and cytosolic SMAD4 protein and SMAD4 mRNA expression in cocultured HuH7 cells. Together these data indicate that hypoxia represses hepcidin expression through inhibition of BMP/SMAD signaling.