Regulation of Iron Homeostasis By PTG-300 Improves Disease Parameters in Mouse Models for Beta-Thalassemia and Hereditary Hemochromatosis

Hepcidin-Ferroportin axis dictates optimal absorption of dietary iron as well as systemic iron levels. This is crucial for providing sufficient iron needed for cellular functions while also preventing iron toxicity. PTG-300 (currently in a Phase 2 clinical study for beta-thalassemia) is a peptide mimetic of natural hepcidin that targets the major iron transporter, ferroportin, and causes its internalization & subsequent degradation. The pharmacodynamic effects of PTG-300 are the reductions in serum iron and transferrin-saturation (TSAT) due to reduced ferroportin expression on cells that store or recycle iron. We chose to demonstrate in two mouse models with iron dysregulation, that our hepcidin mimetics improve disease parameters by correcting dysregulated iron homeostasis. Beta-thalassemia is characterized by an imbalance in alpha-beta globin ratio in erythrocytes due to underlying beta-globin gene mutations. The excess alpha-globin, along with associated heme and iron, form "hemichrome" aggregates that integrate into the membranes of RBCs. The labile iron in these hemichromes generate ROS and are toxic to the cells, causing premature hemolysis of circulating RBCs and reduction in their lifespan. In a mouse model for beta-thalassemia, Hbbth3/+, we investigated the efficacy of a hepcidin mimetic in reducing hemichrome aggregation by limiting iron in the erythroid progenitors, and thereby reducing iron toxicity in RBCs. Subcutaneous injections of 1 mg/kg PN-8772 (analog of PTG-300 which has similar in vitro and in vivo potency) were administered every other day (Q2D) for a period of 4 weeks. At the end of the study, hemichrome aggregates were extracted from RBC membranes, and then analyzed on a TAU gel to quantify the cytoskeleton α-globin band intensities (Casu et al, Blood 2016). Hemichrome aggregates were reduced in groups treated with PN-8772 as compared to untreated controls, with concurrent improvements in hemoglobin and reductions in reticulocytes. Treatment with oral chelator Deferasirox (200 mg/kg; daily) did not show reduction in hemichrome aggregation, while it significantly lowered liver iron-overload. RBCs in Hbbth3/+ mice express aberrant morphologies due to the underlying hemichrome toxicity, similar to the phenotypes expressed in human beta-thalassemia. Chronic treatment with PN-8772 (as described above) also resulted in a significant reduction in aberrant morphologies that are indicative of hemolysis, viz. spherocytes & schistocytes. In a separate study, flow cytometry was used to monitor the survival of RBCs in Hbbth3/+ mice. At the end of 4 weeks of PTG-300 treatment (1 mg/kg, Q2D) the RBCs were marked by an in-life biotinylation method (Schmidt et al, Blood 2013) and subsequently followed over 49 days with continued treatment. There was a significant increase in survival of RBCs as compared to untreated controls. In summary, we demonstrate that by limiting iron in the developing erythroblasts and iron toxicity in RBCs, PTG-300 therapy has the potential to improve the quality of the RBCs and their oxygen carrying capacity, thereby ameliorating anemia. In beta-thalassemia, the clinical presentation includes secondary iron overload in various organs because of hyperabsorption of dietary iron, exacerbated by frequent blood transfusions that are required for management of anemia. Similarly, in hereditary hemochromatosis (HH) there is hyperabsorption of dietary iron leading to primary iron overload. We used a hemochromatosis mouse model (HFE) to demonstrate the effectiveness of PTG-300 therapy in limiting systemic iron toxicity by regulating TSAT and in preventing hyper-iron absorption. The model is characterized by homozygous deletion of HFE with severely low hepcidin levels and consequently very high TSAT (~100%). In this model, a single dose of PTG-300 at 2.5mg/kg reduced TSAT by ~60% at 10-hour post-dose, as compared to untreated controls. Sustained TSAT reduction by chronic treatment will therefore mitigate toxic effects of labile iron. Two weeks of chronic treatment with PTG-300 (2.5 mg/kg, Q2D) effectively prevented iron deposition in the liver. Overall our data suggests that PTG-300 has the potential to be an effective treatment in hemoglobinopathies, like beta-thalassemia, and Hereditary Hemochromatosis, by reducing systemic labile iron toxicity by limiting TSAT, preventing organ iron deposition & improving anemia (in case of thalassemia). Disclosures Taranath: Protagonist Therapeutics: Employment. Bourne:Protagonist Therapeutics: Employment. Zhao:Protagonist Therapeutics: Employment. Frederick:Protagonist Therapeutics: Employment. King:Protagonist Therapeutics: Employment. Liu:Protagonist Therapeutics: Employment.

Download Full-text

Enhanced erythropoiesis in Hfe-KO mice indicates a role for Hfe in the modulation of erythroid iron homeostasis

Blood ◽

10.1182/blood-2010-09-307462 ◽

2011 ◽

Vol 117 (4) ◽

pp. 1379-1389 ◽

Cited By ~ 31

Author(s):

Pedro Ramos ◽

Ella Guy ◽

Nan Chen ◽

Catia C. Proenca ◽

Sara Gardenghi ◽

...

Keyword(s):

Iron Overload ◽

Iron Uptake ◽

Iron Homeostasis ◽

Hereditary Hemochromatosis ◽

Dietary Iron ◽

Erythroid Cells ◽

Hepcidin Expression ◽

Stress Erythropoiesis ◽

Cellular Iron ◽

Cellular Iron Uptake

Abstract In hereditary hemochromatosis, mutations in HFE lead to iron overload through abnormally low levels of hepcidin. In addition, HFE potentially modulates cellular iron uptake by interacting with transferrin receptor, a crucial protein during erythropoiesis. However, the role of HFE in this process was never explored. We hypothesize that HFE modulates erythropoiesis by affecting dietary iron absorption and erythroid iron intake. To investigate this, we used Hfe-KO mice in conditions of altered dietary iron and erythropoiesis. We show that Hfe-KO mice can overcome phlebotomy-induced anemia more rapidly than wild-type mice (even when iron loaded). Second, we evaluated mice combining the hemochromatosis and β-thalassemia phenotypes. Our results suggest that lack of Hfe is advantageous in conditions of increased erythropoietic activity because of augmented iron mobilization driven by deficient hepcidin response. Lastly, we demonstrate that Hfe is expressed in erythroid cells and impairs iron uptake, whereas its absence exclusively from the hematopoietic compartment is sufficient to accelerate recovery from phlebotomy. In summary, we demonstrate that Hfe influences erythropoiesis by 2 distinct mechanisms: limiting hepcidin expression under conditions of simultaneous iron overload and stress erythropoiesis, and impairing transferrin-bound iron uptake by erythroid cells. Moreover, our results provide novel suggestions to improve the treatment of hemochromatosis.

Download Full-text

SLN124, a Galnac-siRNA Conjugate Targeting TMPRSS6, for the Treatment of Iron Overload and Ineffective Erythropoiesis Such As in Beta-Thalassemia

Blood ◽

10.1182/blood-2018-99-110163 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 2340-2340 ◽

Cited By ~ 3

Author(s):

Sandro Altamura ◽

Martina U. Muckenthaler ◽

Sibylle Dames ◽

Christian Frauendorf ◽

...

Keyword(s):

Gene Expression ◽

Iron Overload ◽

Target Gene ◽

Iron Homeostasis ◽

Hereditary Hemochromatosis ◽

Beta Thalassemia ◽

Iron Loading ◽

Ineffective Erythropoiesis ◽

Target Gene Expression ◽

Tissue Iron

Abstract Accumulation of excess iron in tissues causes organ damage and dysfunction and may lead to serious clinical consequences including liver cirrhosis, diabetes, growth retardation and heart failure. Iron overload is a major health threat in iron loading anemias, like beta-thalassemia, myelodysplastic syndrome and in hereditary hemochromatosis. In patients with beta-thalassemia major, iron overload develops due to frequent blood transfusions to control the severe anemia. In addition, iron overload also occurs in patients with beta thalassemia intermedia (non-transfusion dependent beta-thalassemia). In the later cases, iron overload develops through gastrointestinal iron hyperabsorption due to stressed and ineffective erythropoiesis. Importantly, expression of the peptide hormone hepcidin, which is the key modulator in iron homeostasis, is abnormally low and unable to block ferroportin-mediated intestinal iron absorption. In hereditary hemochromatosis, gene defects in the hepcidin-ferroportin axis controlling iron homeostasis, lead to hepatic iron overload. Therefore, in these indications, iron overload is caused by dysregulation or dysfunction of the hepcidin-ferroportin axis. Hepcidin is predominantly produced by the liver and is induced by activation of the BMP/SMAD signaling pathway. Furthermore, hepcidin is under the negative control of the transmembrane protease matriptase-2, encoded by the TMPRSS6 gene. RNA interference is a natural mechanism and a powerful approach for inhibiting the expression of disease-associated genes. Silence Therapeutics has developed short interfering RNA (siRNA) conjugate technology for the selective inhibition of target gene expression in the liver. GalNAc-conjugated siRNAs bind efficiently to the asialoglycoprotein (ASGP) receptor expressed predominantly by hepatocytes thereby providing a highly specific, safe and efficient delivery technology to enable a new class of therapeutic use. Here we present the pharmacological characterization of SLN124, our GalNAc-siRNA conjugate targeting TMPRSS6 expression, in preclinical models. A single subcutaneous administration is sufficient to achieve significant modulation of target gene expression in mice and in non-human primates over several weeks. SLN124 treatment reduces systemic iron levels, transferrin saturation and tissue iron levels in a rodent model for hereditary hemochromatosis type 1. In addition, we report for the first time the therapeutic efficacy of iron restriction by SLN124 in mice with established iron overload both as monotherapy and in combination with an oral iron chelator - current standard of care- over an extended treatment period. The effects of these treatments on red blood cell parameters and tissue iron levels will be presented. In addition, we assessed the therapeutic effects of SLN124 in an animal model for beta-thalassemia intermedia, showing dose-dependent and long-lasting effects on target gene expression as well as on modulation of iron stores and normalization of erythropoiesis and anemia. Safety and tolerability studies in relevant preclinical models confirmed that SLN124 is well tolerated and shows promise as an effective and safe treatment for unmet medical need in iron loading anemias, such as beta-thalassemia. SLN124 is currently in preclinical development. The first in human study is planned to commence in 2019 in patients with beta-thalassemia and in patients with myelodysplastic syndrome. Disclosures Muckenthaler: Novartis: Research Funding. Dames:Silence Therapeutics GmbH: Employment. Frauendorf:Silence Therapeutics GmbH: Employment. Schubert:Silence Therapeutics GmbH: Employment. Aleku:Silence Therapeutics GmbH: Employment. Zügel:Silence Therapeutics GmbH: Employment.

Download Full-text

Does Gene Therapy in Beta Thalassemia Normalize Novel Markers of Ineffective Erythropoiesis and Iron Homeostasis?

Blood ◽

10.1182/blood-2019-129658 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 816-816 ◽

Cited By ~ 1

Author(s):

Alexis A. Thompson ◽

Tomas Ganz ◽

Mary Therese Forsyth ◽

Elizabeta Nemeth ◽

Sherif M. Badawy

Keyword(s):

Gene Therapy ◽

Stem Cell ◽

Iron Overload ◽

Serum Ferritin ◽

Research Funding ◽

Iron Homeostasis ◽

Beta Thalassemia ◽

Ineffective Erythropoiesis ◽

Liver Iron ◽

Equity Ownership

BACKGROUND: Ineffective erythropoiesis in thalassemia alters iron homeostasis, predisposing to systemic iron overload. Successful allogeneic hematopoietic stem cell transplantation (HSCT) in thalassemia major corrects anemia, should eliminate ineffective erythropoiesis (IE) and normalize iron homeostasis (IH). Whether gene therapy (GT) will fully correct IE and IH is not known. This cross-sectional observational study evaluated the iron status of patients with beta thalassemia following HSCT or GT, and compared them with cohorts of patients with thalassemia intermedia (TI) or transfusion-dependent thalassemia (TDT) using recently introduced biomarkers along with imaging studies and other clinical assessments to better understand and characterize IE and IH across groups. METHODS: We evaluated a convenience sample of 29 participants with beta thalassemia (median age 25 years, IQR 21-35; females 55%; Asian 52%). Participants in the HSCT (n=6) and GT (n=10) groups were evaluated on average 116.5 and 46.9 months following cell infusion, respectively. TDT patients (n= 9) were evaluated pre-transfusion and off iron chelation for at least 7 days, and TI (n=4) were un-transfused or not transfused in >3 years. Clinical lab assessments and MRI R2*/ T2* to assess heart and liver iron burden including post-processing, were performed using local clinical protocols. ELISAs for hepcidin, erythroferrone (Erfe) and GDF-15 were performed in a blinded manner. RESULTS: Median values for all IE and IH parameters tested were normal in the HSCT group, and were significantly lower than in all other groups. There were significant differences among all groups for hemoglobin (p=0.003), erythropoietin (Epo) (p=0.03), serum ferritin (SF) (p=0.01), transferrin (p=0.006), soluble transferrin receptor (sTfR) (p=0.02), serum hepcidin: serum ferritin (H:F) ratio (p=0.006), Erfe (p=0.001), GDF15 (p=0.003), and liver iron content (LIC) by MRI R2* (p=0.02). H:F ratio, a surrogate for predisposition to systemic iron loading, inversely correlated with Erfe (rs= -0.85, p<0.0001), GDF15 (rs= -0.69, p=0.0001) and liver R2* (rs= -0.66, p=0.0004). In a multivariate analysis, adjusted for gender and race, H:F ratio and Epo levels predicted Erfe and GDF15 (p=0.05 and p=0.06; p=0.01 and p=0.05), respectively. Even after excluding GT patients that are not transfusion independent (N=2), SF, Epo, sTfR and hepcidin remain abnormal in the GT group, and there were no significant differences in these parameters between GT and TDT. However, novel biomarkers of IH and IE suggested lower ineffective erythropoiesis in GT compared to TDT (median (IQR) Erfe, 12 (11.6-25.2) vs. 39.6 (24.5-54.7), p=0.03; GDF15, 1909.9 (1389-4431) vs. 8906 (4421-12331), p=0.02), respectively. Erfe and GDF15 were also lower in GT compared to TI, however these differences did not reach statistical significance. There were no differences in hepcidin, ferritin, or H:F by race, however Erfe and GDF15 were significantly lower in Asians compared to non-Asians (p=0.006 and p=0.02, respectively). CONCLUSION: Nearly 4 years post infusion, most subjects with TDT treated with GT are transfusion independent with near normal hemoglobin, however, studies in this limited cohort using conventional measures suggest IE and IH improve, particularly when transfusion support is no longer needed, however they remain abnormal compared to HSCT recipients, who using these parameters appear to be cured. STfR did not detect differences, however GDF15 and Erfe were more sensitive assays that could demonstrate significant improvement in IE and IH with GT compared to TDT. Contribution to IE by uncorrected stem cell populations post GT cannot be determined. Transduction enhancement and other recent improvements to GT may yield different results. Longitudinal studies are needed to determine if thalassemia patients treated with GT will have ongoing IE predisposing to systemic iron overload. Disclosures Thompson: bluebird bio, Inc.: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Baxalta: Research Funding. Ganz:Intrinsic LifeSciences: Consultancy, Equity Ownership. Nemeth:Intrinsic LifeSciences: Consultancy, Equity Ownership; Silarus Therapeutics: Consultancy, Equity Ownership; Keryx: Consultancy; Ionis Pharmaceuticals: Consultancy; La Jolla Pharma: Consultancy; Protagonist: Consultancy.

Download Full-text

Down Regulation of Hepcidin and Interleukin 1-Alpha in Pbmc from Patients with Beta thalassemia

Blood ◽

10.1182/blood.v112.11.2880.2880 ◽

2008 ◽

Vol 112 (11) ◽

pp. 2880-2880

Author(s):

Maria-Eliana Lai ◽

Stefania Vacquer ◽

Maria Paola Carta ◽

Claudia Mulas ◽

Pierluigi Cocco ◽

...

Keyword(s):

Iron Overload ◽

Iron Homeostasis ◽

Mononuclear Cells ◽

Interleukin 1 ◽

Diagnostic Tools ◽

Beta Thalassemia ◽

Blood Transfusions ◽

Mrna Levels ◽

Down Regulation ◽

Hepcidin Mrna

Abstract Thalassemia is an inherited blood disease characterized by low levels or absence of normal globin chains. Severe forms of thalassemia, thalassemia major (TM), require regular blood transfusions, the main cause of secondary hemosyderosis. However, iron overload is a potential complication, even in patients (pts) with thalassemia intermedia (TI), who do not require transfusions. Among them, iron overload is mainly the result of an excessive absorption of dietary iron, caused by a down-regulation of hepcidin, an hepatic hormone that acts as a major regulator of systemic iron homeostasis. Very low mRNA levels of hepcidin have been reported in urine as well as in liver biopsies from patients with TI. It has been also reported that, interleukin-1 alpha (IL-1α) stimulates hepcidin transcription, raising the question as to whether a down-regulation of this cytokine may be responsible, at least partially, for the excessive iron absorption occurring in patients with TI. Here, we assessed whether IL-1α was involved in hepcidin regulation in β-thalassemia. Peripheral blood mononuclear cells (PBMCs) were isolated from 6 TM pts, 8 TI pts and 6 controls. mRNA was obtained from PBMCs by RT-PCR. Hepcidin mRNA levels were reduced in both TM and TI pts when compared to the age matched normal controls. Neverthless, hepcidin mRNA levels were significantly lower in TI pts, as compared to TM pts receiving regular blood transfusions. Among TI pts lower hepcidin mRNA level was associated with lower level of IL-α. Tumor necrosis factor alpha (TNF-α) does not seem to be involved in the regulation of hepcidin transcription. Interestingly, the levels of mRNA expression of acyl-CoA-cholesterol acyltransferase (ACAT), the enzyme responsible for intracellular cholesterol ester accumulation, and thus, for atherosclerotic plaque formation were strongly induced in PBMCs in TI pts. These results suggest that PBMCs hepcidin and IL-1-α measurements could possibly be used in the future as simple, ease and sensible diagnostic tools for the detection of iron overload in patients with thalassemia. ACAT expression may even be used as therapeutic target in preventing atherosclerotic complications such as pulmonary thromboembolism, cerebral thrombosis, and leg ulcers. frequently occurring in such patients.

Download Full-text

Frequency of hereditary hemochromatosis gene mutations and their effects on iron overload among beta thalassemia patients of Chennai residents

AIMS Molecular Science ◽

10.3934/molsci.2021018 ◽

2021 ◽

Vol 8 (4) ◽

pp. 233-247

Author(s):

Bhuvana Selvaraj ◽

◽

Sangeetha Soundararajan ◽

Shettu Narayanasamy ◽

Ganesan Subramanian ◽

...

Keyword(s):

Iron Overload ◽

Iron Status ◽

Globin Gene ◽

Hereditary Hemochromatosis ◽

Gene Mutations ◽

Autosomal Recessive Disorder ◽

Thalassemia Major ◽

Organ Damage ◽

Beta Thalassemia ◽

Hemochromatosis Gene

<abstract> <p>Hereditary Hemochromatosis (HH) is an autosomal recessive disorder of iron metabolism associated with <italic>HFE</italic> gene mutations, characterized by increased iron absorption and accumulation leading to multi-organ damage caused by iron overload toxicity. Beta thalassemia is caused by a mutation in the human beta globin gene. Imbalanced production of globin chain results in beta thalassemia, where the unpaired alpha chains precipitates in red cell precursors leading to ineffective erythropoiesis and reduced RBC survival. Both HH and beta thalassemia condition results in rapid accumulation of iron lead to iron overload in tissues and organs. The study aims to analyze the frequency of <italic>HFE</italic> variants among beta thalassemia cases and their effect on iron overload. The frequency of three <italic>HFE</italic> variants C282Y, H63D, S65C was analyzed by PCR RFLP method among Beta Thalassemia Trait (BTT) (n = 203), Beta Thalassemia Major (BTM) (n = 19) and age and sex-matched control samples (n = 200). The present study furnished allele frequency of H63D variant in BTT, BTM and controls 8.13, 15.8 and 6% respectively. Ten out of 33 heterozygous H63D variants exhibited iron overload with higher ferritin levels indicating <italic>HFE</italic> variant might aggravate the absorption of iron. The C282Y variant was present in heterozygous state in 1 case among beta thalassemia carriers. The C282Y variant was absent among BTM and control cases. S65C <italic>HFE</italic> variant was absent in the present study. Iron overload was completely absent in the control cases among all three <italic>HFE</italic> genotypes. Hence it is inferred from the present investigation, analysis of <italic>HFE</italic> genes and iron status will remarkably help to reason out the probable reason behind the iron status and support in proper management of beta thalassemia cases.</p> </abstract>

Download Full-text

Management of Iron Overload in Beta-Thalassemia Patients: Clinical Practice Update Based on Case Series

International Journal of Molecular Sciences ◽

10.3390/ijms21228771 ◽

2020 ◽

Vol 21 (22) ◽

pp. 8771

Author(s):

Valeria Maria Pinto ◽

Gian Luca Forni

Keyword(s):

Iron Overload ◽

Malignant Transformation ◽

Chelation Therapy ◽

Prolonged Exposure ◽

Case Series ◽

Iron Toxicity ◽

Beta Thalassemia ◽

Human Organism ◽

Noninvasive Methods ◽

Toxic Agent

Thalassemia syndromes are characterized by the inability to produce normal hemoglobin. Ineffective erythropoiesis and red cell transfusions are sources of excess iron that the human organism is unable to remove. Iron that is not saturated by transferrin is a toxic agent that, in transfusion-dependent patients, leads to death from iron-induced cardiomyopathy in the second decade of life. The availability of effective iron chelators, advances in the understanding of the mechanism of iron toxicity and overloading, and the availability of noninvasive methods to monitor iron loading and unloading in the liver, heart, and pancreas have all significantly increased the survival of patients with thalassemia. Prolonged exposure to iron toxicity is involved in the development of endocrinopathy, osteoporosis, cirrhosis, renal failure, and malignant transformation. Now that survival has been dramatically improved, the challenge of iron chelation therapy is to prevent complications. The time has come to consider that the primary goal of chelation therapy is to avoid 24-h exposure to toxic iron and maintain body iron levels within the normal range, avoiding possible chelation-related damage. It is very important to minimize irreversible organ damage to prevent malignant transformation before complications set in and make patients ineligible for current and future curative therapies. In this clinical case-based review, we highlight particular aspects of the management of iron overload in patients with beta-thalassemia syndromes, focusing on our own experience in treating such patients. We review the pathophysiology of iron overload and the different ways to assess, quantify, and monitor it. We also discuss chelation strategies that can be used with currently available chelators, balancing the need to keep non-transferrin-bound iron levels to a minimum (zero) 24 h a day, 7 days a week and the risk of over-chelation.

Download Full-text

A High Through-Put Screen Identifies MCP-1 (CCL2) As a Novel Regulator of Iron Homeostasis and a Modifier of Hereditary Hemochromatosis Disease Severity

Blood ◽

10.1182/blood.v118.21.685.685 ◽

2011 ◽

Vol 118 (21) ◽

pp. 685-685

Author(s):

Martina U. Muckenthaler ◽

Maja Vujic Spasic ◽

Katarzyna Mleczko-Sanecka ◽

Mingang Zhu ◽

Rainer Pepperkok ◽

...

Keyword(s):

Iron Overload ◽

Mrna Expression ◽

Disease Severity ◽

Iron Homeostasis ◽

Expression Profiles ◽

Hereditary Hemochromatosis ◽

Transferrin Saturation ◽

Human Cells ◽

Liver Iron ◽

Deficient Mice

Abstract Abstract 685 To identify genes that modify the severity of human iron disorders we pre-selected 74 genes from gene expression profiles of cells and tissues with altered iron levels and assessed whether siRNA-mediated knock-down of these genes affects uptake of transferrin, a key cellular process to acquire iron. This screen identifies the monocyte chemoattractant protein-1 (MCP-1), also known as CCL2, as a critical suppressor of transferrin receptor mRNA expression in human cells. We next analyzed CCL2-deficient mice and demonstrate profound alterations of parameters of systemic iron homeostasis. Specifically, CCL2 knock-out mice show decreased serum iron levels and transferrin saturation, strong iron-overload in the spleen and duodenum as well as mild iron accumulation in the liver. Iron imbalance in CCL2−/− mice is unlikely explained by an impairment of the major control system of systemic iron homeostasis, the hepcidin/ferroportin regulatory system: hepcidin mRNA expression is unaltered and splenic ferroportin protein expression is strongly increased in CCL2−/− mice, as would be expected as a consequence of splenic iron overload. We speculate that increased iron absorption from the plasma, possibly mediated by inappropriately high levels of TfR1 in the spleen, duodenum and liver, may be responsible for tissue iron overload. It is of note that CCL2 levels are strongly decreased in Hfe-deficient mice and patients with Hfe-associated Hereditary Hemochromatosis (HH). We therefore asked whether CCL2 levels could modify disease severity of HH. Analysis of 51 HH patients, all homozygous for the C282Y HFE mutation, confirms significantly lower MCP-1 levels in the serum compared to a group of 23 sex- and age-matched normal controls. Importantly, CCL2 levels in HH patients show a significant negative correlation with liver iron overload at the time point of diagnosis. Furthermore, low CCL2 concentrations are significantly associated with the HLA-A3 genotype and the CD8+ T lymphocyte phenotype, both traits previously shown to correlate with iron overload in HH patients. These patient data and the data from CCL2-deficient mice suggest that appropriate CCL2 expression is required to prevent iron overload. Taken together our data demonstrate the power of siRNA screens to identify novel regulators of iron metabolism in human cells that are critically involved in maintaining systemic iron homeostasis in the mouse and that play a role in modifying hepatic iron overload in the frequent iron overload disorder Hereditary Hemochromatosis. Disclosures: No relevant conflicts of interest to declare.

Download Full-text

An Essential Role For Transferrin Receptor 2 In Erythropoiesis During Iron Restriction

Blood ◽

10.1182/blood.v122.21.429.429 ◽

2013 ◽

Vol 122 (21) ◽

pp. 429-429

Author(s):

Daniel F Wallace ◽

Cameron J McDonald ◽

Eriza S Secondes ◽

Lesa Ostini ◽

Gautam Rishi ◽

...

Keyword(s):

Iron Deficiency ◽

Iron Overload ◽

Iron Deficiency Anemia ◽

Transferrin Receptor ◽

Iron Homeostasis ◽

Hereditary Hemochromatosis ◽

Deficiency Anemia ◽

Erythroid Cells ◽

Iron Restriction ◽

Extramedullary Erythropoiesis

Abstract Iron deficiency and iron overload are common clinical conditions that impact on the health and wellbeing of up to 30% of the world’s population. Understanding mechanisms regulating iron homeostasis will provide improved strategies for treating these disorders. The liver-expressed proteins matriptase-2 (encoded by TMPRSS6), HFE and transferrin receptor 2 (TFR2) play important and opposing roles in systemic iron homeostasis by regulating expression of the iron regulatory hormone hepcidin. Mutations in TMPRSS6 lead to iron refractory iron deficiency anemia, whereas mutations in HFE and TFR2 lead to the iron overload disorder hereditary hemochromatosis. To elucidate the competing roles of these hepcidin regulators, we created mice lacking matriptase-2, Hfe and Tfr2. Tmprss6 -/-/Hfe-/-/Tfr2-/- mice had iron deficiency anemia resulting from hepatic hepcidin over-expression and activation of Smad1/5/8, indicating that matriptase-2 predominates over Hfe and Tfr2 in hepcidin regulation. Surprisingly, this anemia was more severe than in the Tmprss6-/- mice, demonstrated by more extensive alopecia, lower hematocrit and significant extramedullary erythropoiesis in the spleen. There was increased expression of erythroid-specific genes in the spleens of Tmprss6-/-/Hfe-/-/Tfr2-/- mice, consistent with the extramedullary erythropoiesis. Expression of Tfr2 but not Hfe in the spleen was increased in the Tmprss6-/- mice compared to wild type and correlated with the expression of erythroid genes, suggesting that Tfr2 is expressed in erythroid cells. Further analysis of gene expression in the bone marrow suggests that the loss of Tfr2 in the erythroid cells of Tmprss6-/-/Hfe-/-/Tfr2-/- mice causes a delay in the differentiation process leading to a more severe phenotype. In conclusion, our results indicate that Hfe and Tfr2 act upstream of matriptase-2 in hepcidin regulation or in a way that is overridden when matriptase-2 is deleted. These results indicate that inhibition of matriptase-2 would be useful in the treatment of iron overload conditions such as hereditary hemochromatosis. We have also identified a novel role for Tfr2 in erythroid differentiation that is separate from its canonical role as a regulator of iron homeostasis in the liver. This important role of Tfr2 in erythropoiesis only becomes apparent during conditions of iron restriction. Our results provide novel insights into mechanisms regulating and linking iron homeostasis and erythropoiesis. Disclosures: No relevant conflicts of interest to declare.

Download Full-text

Hepatic Iron Overload following Liver Transplantation from a C282Y/H63D Compound Heterozygous Donor

Case Reports in Hepatology ◽

10.1155/2018/4298649 ◽

2018 ◽

Vol 2018 ◽

pp. 1-4 ◽

Cited By ~ 1

Author(s):

E. Veitsman ◽

E. Pras ◽

O. Pappo ◽

A. Arish ◽

R. Eshkenazi ◽

...

Keyword(s):

Iron Overload ◽

Genetic Disease ◽

Sclerosing Cholangitis ◽

Iron Homeostasis ◽

Hereditary Hemochromatosis ◽

Compound Heterozygous ◽

Primary Role ◽

Hepatic Iron Overload ◽

Liver Biopsies ◽

First Time

Hereditary hemochromatosis (HH) is a genetic disease associated with progressive iron overload, eventually leading in some cases to damage of parenchymal organs, such as the liver, pancreas, and heart. Although the gene had been identified (HFE), HH pathogenesis remains to be fully elucidated. We report here, for the first time, a case of inadvertent transplantation of a liver from a donor with C282Y/H63D compound heterozygosity into a nonhemochromatotic 19-year-old Caucasian male recipient with primary sclerosing cholangitis. Progressive iron overload occurred over 1.5 years, as observed in liver biopsies and iron studies, after ruling out secondary causes of iron overload. This case strengthens the hypothesis that the liver, rather than the small intestine, plays a primary role in the maintenance of iron homeostasis.

Download Full-text

Expression of hepcidin in hereditary hemochromatosis: evidence for a regulation in response to the serum transferrin saturation and to non-transferrin-bound iron

Blood ◽

10.1182/blood-2002-11-3610 ◽

2003 ◽

Vol 102 (1) ◽

pp. 371-376 ◽

Cited By ~ 167

Author(s):

Sven G. Gehrke ◽

Hasan Kulaksiz ◽

Thomas Herrmann ◽

Hans-Dieter Riedel ◽

Karin Bents ◽

...

Keyword(s):

Iron Overload ◽

Serum Ferritin ◽

Iron Homeostasis ◽

Iron Status ◽

Hereditary Hemochromatosis ◽

Transferrin Saturation ◽

Serum Transferrin ◽

Transcript Levels ◽

Hepcidin Expression

Abstract Experimental data suggest the antimicrobial peptide hepcidin as a central regulator in iron homeostasis. In this study, we characterized the expression of human hepcidin in experimental and clinical iron overload conditions, including hereditary hemochromatosis. Using quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), we determined expression of hepcidin and the most relevant iron-related genes in liver biopsies from patients with hemochromatosis and iron-stain-negative control subjects. Regulation of hepcidin mRNA expression in response to transferrin-bound iron, non-transferrin-bound iron, and deferoxamine was analyzed in HepG2 cells. Hepcidin expression correlated significantly with serum ferritin levels in controls, whereas no significant up-regulation was observed in patients with hemochromatosis despite iron-overload conditions and high serum ferritin levels. However, patients with hemochromatosis showed an inverse correlation between hepcidin transcript levels and the serum transferrin saturation. Moreover, we found a significant correlation between hepatic transcript levels of hepcidin and transferrin receptor-2 irrespective of the iron status. In vitro data indicated that hepcidin expression is down-regulated in response to non-transferrin-bound iron. In conclusion, the presented data suggest a close relationship between the transferrin saturation and hepatic hepcidin expression in hereditary hemochromatosis. Although the causality is not yet clear, this interaction might result from a down-regulation of hepcidin expression in response to significant levels of non-transferrin-bound iron. (Blood. 2003;102:371-376)

Download Full-text