Identification of erythroferrone as an erythroid regulator of iron metabolism

Mechanism and regulation of iron absorption throughout the life cycle

BACKGROUND

Iron plays a crucial role through various life stages of human. Iron homeostasis is primarily regulated by iron absorption which is mediated via divalent metal-ion transporter 1 (DMT1), and iron export protein ferroportin (FPN), as there is no active pathway for iron excretion from the body. Recent studies have shown that the magnitude of iron absorption changes through various life stages to meet changing iron requirements.

AIM OF REVIEW

This review aims to provide an overview of recent researches on the regulation of iron absorption throughout mammalian life cycle, with the potential to reveal novel molecules and pathways at special stage of life. Such insights may pave the way for new treatments for disorders associated with aberrant iron homeostasis in the future.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review first summarize the mechanism and regulation of iron absorption throughout various life stages, highlighting that regulatory mechanisms have developed to precisely align iron absorption to iron requirements. In adults, iron absorption is enhanced when body is deficient of iron, conversely, iron absorption is reduced when iron demand decreases via systemic regulator Hepcidin and cellular regulation. In the elderly, age-related inflammation, hormonal changes, and chronic diseases may affect the production of Hepcidin, affecting iron absorption. In infants, intestinal iron absorption and its regulatory mechanism are different from that in adults and there might be an alternative pathway independent of DMT1 and FPN due to high iron absorption. Unique to the fetus, iron is absorbed from maternal stores for its own use through the placenta and is regulated by maternal iron status. This review also proposes directions for further studies, offering promising avenues for developing new treatments for disorders associated with aberrant iron homeostasis.

Mechanism-Based Pharmacokinetic/Pharmacodynamic Modeling of Erythroferrone in Anemic Rats with Chronic Kidney Disease and Chemotherapy-Induced Anemia: An Early Biomarker for Hemoglobin Response and rHuEPO Hyporesponsiveness

Erythroferrone (ERFE) has emerged as a potential biomarker for the erythropoiesis response following recombinant human erythropoietin (rHuEPO) treatment. While the association between ERFE and hemoglobin (HGB) response to rHuEPO is well-established in nonanemic conditions, such correlation and ERFE kinetics in anemic states remain unclear. We employed two rat models of anemia, chronic kidney disease (CKD) anemia and chemotherapy-induced anemia (CIA), to determine ERFE kinetics and its correlation with HGB responses after rHuEPO administration. The key factors influencing ERFE kinetics were characterized using a PK/PD modeling approach and supported by experimentation. Following rHuEPO injection, ERFE induction was diminished in anemic rats compared with that of healthy rats, primarily attributed to the reduced precursor cell mass and impaired rHuEPO responsiveness. The early increase in ERFE at 4 h post administration allows for the prompt prediction of HGB response and rHuEPO hyporesponsiveness in anemic rats. Consequently, the ERFE-based dose adjustment resulted in a rHuEPO-sparing effect in CKD rats. This strategy is expected to be translatable to anemic patients, potentially reducing rHuEPO doses and mitigating HGB overshooting.

Genetic iron overload aggravates, and pharmacological iron restriction improves, MDS pathophysiology in a preclinical study

ABSTRACT

Although iron overload is a common feature in myelodysplastic syndromes (MDS), it remains unclear how iron excess is detrimental for disease pathophysiology. Taking advantage of complementary approaches, we analyzed the impact of iron overload and restriction achieved through genetic activation of ferroportin (FPN) via the C326S mutation (FPNC326S) and pharmacologic inhibition (vamifeport) of the iron exporter FPN, respectively, in a MDS mouse model. Although FPNC326S-induced iron overload did not significantly improve the late stages of erythroid maturation, vamifeport-mediated iron restriction ameliorated anemia and red blood cell maturation in MDS mice, through the reduction of oxidative stress and apoptosis in erythroid progenitors. Iron overload aggravated, and restriction alleviated, reactive oxygen species formation, DNA damage, and cell death in hematopoietic stem and progenitor cells (HSPCs), resulting in altered cell survival and quality. Finally, myeloid bias, indicated by expanded bone marrow myeloid progenitors and circulating immature myeloid blasts, was exacerbated by iron excess and attenuated by iron restriction. Overall, vamifeport treatment resulted in improved anemia and significant survival increment in MDS mice. Interestingly, the combined therapy with vamifeport and the erythroid maturation agent luspatercept has superior effect in improving anemia and myeloid bias as compared with single treatments and offers additive beneficial effects in MDS. Our results prove, to our knowledge, for the first time in a preclinical model, that iron plays a pathologic role in transfusion-independent MDS. This is likely aggravated by transfusional iron overload, as suggested by observations in the FPNC326SMDS model. Ultimately, the beneficial effects of pharmacologic FPN inhibition uncovers the therapeutic potential of early prevention of iron toxicity in transfusion-independent MDS.

In defence of ferroptosis

Rampant phospholipid peroxidation initiated by iron causes ferroptosis unless this is restrained by cellular defences. Ferroptosis is increasingly implicated in a host of diseases, and unlike other cell death programs the physiological initiation of ferroptosis is conceived to occur not by an endogenous executioner, but by the withdrawal of cellular guardians that otherwise constantly oppose ferroptosis induction. Here, we profile key ferroptotic defence strategies including iron regulation, phospholipid modulation and enzymes and metabolite systems: glutathione reductase (GR), Ferroptosis suppressor protein 1 (FSP1), NAD(P)H Quinone Dehydrogenase 1 (NQO1), Dihydrofolate reductase (DHFR), retinal reductases and retinal dehydrogenases (RDH) and thioredoxin reductases (TR). A common thread uniting all key enzymes and metabolites that combat lipid peroxidation during ferroptosis is a dependence on a key cellular reductant, nicotinamide adenine dinucleotide phosphate (NADPH). We will outline how cells control central carbon metabolism to produce NADPH and necessary precursors to defend against ferroptosis. Subsequently we will discuss evidence for ferroptosis and NADPH dysregulation in different disease contexts including glucose-6-phosphate dehydrogenase deficiency, cancer and neurodegeneration. Finally, we discuss several anti-ferroptosis therapeutic strategies spanning the use of radical trapping agents, iron modulation and glutathione dependent redox support and highlight the current landscape of clinical trials focusing on ferroptosis.

Cell-free hemoglobin released from hemolysis induces programmed cell death through iron overload and oxidative stress in grass carp (Ctenopharyngodon idella)

Intravascular hemolysis releases hemoglobin (Hb) from red blood cells under specific conditions, yet the effect of hemolysis in aquaculture systems remain poorly understood. In this study, a continuous hemolysis model for grass carp was established by injection of phenylhydrazine (PHZ) to investigate the mechanistic impacts of sustained hemolysis. PHZ-induced hemolysis altered liver color, and subsequent hematoxylin and eosin staining revealed substantial Hb accumulation in the head kidney, accompanied by inflammatory cell infiltration and vacuolization in liver tissue. Quantitative real-time PCR and western blotting confirmed that PHZ treatment significantly upregulated Real-time fluorescence quantitative PCR and western blot confirmed that PHZ treatment significantly up-regulated the expression of iron metabolism-related genes and proteins, including transferrin (Tf), ferritin, ferroportin 1 (FPN1), transferrin receptor 1 (TfR1), nuclear receptor coactivator 4 (NCOA4), divalent metal transporter 1 (DMT1), and six-transmembrane epithelial antigen of prostate 3 (STEAP3). Further investigation of PHZ-induced hemolysis effects on tissues showed that inflammation- and antioxidant enzyme-related genes in the liver and head kidney were significantly upregulated, indicating that hemolysis activated the antioxidant system and intensified inflammatory responses. Perls' staining revealed iron deposition in the head kidney and liver at ten and fourteen days post-PHZ injection. Moreover, β-galactosidase staining and transmission electron microscopy showed increased cellular senescence and mitochondrial damage, respectively, as a result of PHZ-induced hemolysis. In vitro assays with hemin treatment demonstrated increased Fe2+ content in CIK and L8824 cells, which induced oxidative stress, upregulated iron metabolism and inflammatory genes, and ultimately led to cell death. These findings suggest that excessive Hb release during sustained hemolysis leads to iron overload, elevates reactive oxygen species production, disrupts antioxidant balance, and ultimately causes cellular damage.

Mesangial cell hypercellularity and iron accumulation in the kidney associated with administration of a sickle hemoglobin modulator in CD-1 mice

The kidney plays an important role in iron homeostasis and mesangial cells (MCs) are phagocytic cells important for glomerular homeostasis. Sickle hemoglobin (HbS) modulators are promising clinical candidates for treatment of sickle cell disease. Although they prevent disease pathophysiology of HbS polymerization and red blood cell (RBC) sickling by increasing hemoglobin oxygen affinity, higher oxygen affinity can also cause transient tissue hypoxia with compensatory increases in erythropoiesis and subsequent increases in RBC turnover. CD-1 mice treated with an HbS modulator for 2 weeks developed higher RBC mass, increased erythropoiesis, and, by 1 month, deposition of intracellular pigments in renal tubular and parietal epithelium. In addition, in mice treated for 26 weeks, pigment was observed in MCs, which was accompanied by glomerular cell aggregates (MC hypercellularity) and tubulo-interstitial inflammation. The pigment was confirmed by Perl's iron staining and transmission electron microscopy (TEM) to be iron-containing proteins. Glomerular cell aggregates were confirmed to be MCs by TEM, and Ki-67 immunolabeling suggested that MC hypercellularity was due to proliferation. Collectively, these findings, along with iron-containing proteins in livers and spleens, suggested that iron overload secondary to increased RBC turnover led to increased renal iron reabsorption. While both MC hypercellularity and tubulo-interstitial inflammation were thought to be responses to long-term accumulation of iron, the former was considered a homeostatic response to eliminate iron, and maintain glomerular structure and function, while the latter was more consistent with an iron-catalyzed oxidative stress response. To our knowledge, this is the first report of MC hypercellularity in a preclinical toxicity study.

Testosterone and Erythrocyte Lifespan

CONTEXT

Endogenous and exogenous androgens increase circulating erythrocytes and hemoglobin but their effects on erythrocyte lifespan is not known.

OBJECTIVE

To investigate androgen effects on immature and mature erythrocyte lifespan in humans and mice using novel nonradioactive minimally invasive methods.

DESIGN

Human erythrocyte lifespan was estimated using alveolar carbon monoxide concentration and blood hemoglobin in Levitt's formula in hypogonadal or transgender men before and up to 18 weeks after commencing testosterone (T) treatment. Erythrocyte lifespan was estimated in androgen receptor knockout and wild-type mice after T or DHT treatment of intact females or orchidectomized males using in vivo biotin labelling of erythrocyte surface epitopes for reticulocytes (Ter119+CD71+) and 2 markers of erythrocytes (CD45-, Ter119+CD71-) monitoring their blood disappearance rate by flow cytometry.

RESULTS

Before treatment, hypogonadal and transgender men had marked reduction in erythrocyte lifespan compared with controls. T treatment increased erythrocyte lifespan at 6 weeks but returned to pretreatment levels at 18 weeks, whereas serum T and blood hemoglobin were increased by T treatment remaining elevated at 18 weeks. In mice, T and DHT treatment had higher erythrocyte (but not reticulocyte) lifespan but neither orchidectomy nor androgen receptor inactivation significantly influenced erythrocyte or reticulocyte lifespan.

CONCLUSION

We conclude that hypogonadal men have reduced erythrocyte lifespan and acute androgen-induced increase in circulating erythrocyte lifespan may contribute to the well-known erythropoietic effects of androgens, but longer term effects require further investigation to determine how much they contribute to androgen-induced increases in circulating hemoglobin.

Transgenic augmentation of erythroferrone in mice ameliorates anemia in adenine-induced chronic kidney disease

Anemia is a common and disabling complication of chronic kidney disease (CKD). Current therapies can be burdensome, and full correction of anemia is limited by cardiovascular side effects. New approaches that may offer additional therapeutic options are needed. We explored the anti-anemic effects of erythroferrone, an erythroid hormone that induces iron mobilization by suppressing the master iron-regulatory hormone hepcidin. In a preclinical murine model of adenine-induced CKD, transgenic augmentation of erythroferrone mobilized iron, increased hemoglobin concentrations by approximately 2 g/dl, and modestly improved renal function without affecting systemic or renal inflammation, fibrosis, or markers of mineral metabolism. This study supports the concept that therapeutic augmentation of erythroferrone is a promising approach for alleviating CKD-associated anemia.

Iron overload in acquired sideroblastic anemias and MDS: pathophysiology and role of chelation and luspatercept

Besides transfusion therapy, ineffective erythropoiesis contributes to systemic iron overload in myelodysplastic syndromes with ring sideroblasts (MDS-RS) via erythroferrone-induced suppression of hepcidin synthesis in the liver, leading to increased intestinal iron absorption. The underlying pathophysiology of MDS-RS, characterized by disturbed heme synthesis and mitochondrial iron accumulation, is less well understood. Several lines of evidence indicate that the mitochondrial transporter ABCB7 is critically involved. ABCB7 is misspliced and underexpressed in MDS-RS, due to somatic mutations in the splicing factor SF3B1. The pathogenetic significance of ABCB7 seems related to its role in stabilizing ferrochelatase, the enzyme incorporating iron into protoporphyrin IX to make heme. Although iron-related oxidative stress is toxic, many patients with MDS do not live long enough to develop clinical complications of iron overload. Furthermore, it is difficult to determine the extent to which iron overload contributes to morbidity and mortality in older patients with MDS, because iron-related complications overlap with age-related medical problems. Nevertheless, high-quality registry studies showed that transfusion dependency is associated with the presence of toxic iron species and inferior survival and confirmed a significant survival benefit of iron chelation therapy. The most widely used iron chelator in patients with MDS is deferasirox, owing to its effectiveness and convenient oral administration. Luspatercept, which can reduce SMAD2/SMAD3-dependent signaling implicated in suppression of erythropoiesis, may obviate the need for red blood cell transfusion in MDS-RS for more than a year, thereby diminishing further iron loading. However, luspatercept cannot be expected to substantially reduce the existing iron overload.

Serum hepcidin recalibrated values in Mexican schoolchildren by demographic characteristics, nutritional and infection/inflammation status

Hepcidin production is regulated by iron concentration, erythropoietic activity, and inflammation. There is no reference method for determining its levels, but results obtained through various methods strongly correlate and can be compared using recalibration equations.

OBJECTIVE

To describe recalibrated serum hepcidin values at different percentiles in schoolchildren, considering age, sex, inflammatory processes, H. pylori infection, and iron status.

METHODS

Secondary analysis of data incorporating information on inflammation, H. pylori infection, and iron status of 349 schoolchildren. Hepcidin analysis was performed using a competitive ELISA, and recalibrated hepcidin values were calculated using the inverse of the linear regression model equation obtained by van der Vorm et al. Results: Recalibrated hepcidin values were lower than non-calibrated values. In schoolchildren without infection/inflammation and without iron deficiency, recalibrated values at the 50th percentile (25th-75th) were 4.89 ng/mL (2.68-8.42). For schoolchildren without infection/inflammation but with iron deficiency, recalibrated values were 2.34 ng/mL (1.10-6.58), the lowest hepcidin values observed. The highest values were found in the group with infection/inflammation, regardless of iron deficiency status.

CONCLUSIONS

Recalibrated hepcidin values were lower than non-calibrated values. The highest values were observed in schoolchildren with infectious or inflammatory processes, and the lowest values were observed in schoolchildren with iron deficiency but only in the absence of infectious or inflammatory processes. Using recalibrated hepcidin values allows comparison between data obtained using different analytical methods.

Erythropoietin enhances iron bioavailability in HepG2 cells by downregulating hepcidin through mTOR, C/EBPα and HIF-1α

The regulation of iron (Fe) levels is essential to maintain an adequate supply for erythropoiesis, among other processes, and to avoid possible toxicity. The liver-produced peptide hepcidin is regarded as the main regulator of Fe absorption in enterocytes and release from hepatocytes and macrophages, as it impairs Fe export through ferroportin. The glycoprotein erythropoietin (Epo) drives erythroid progenitor survival and differentiation in the bone marrow, and has been linked to the mobilization of Fe reserves necessary for hemoglobin production. Herein we show that Epo inhibits hepcidin expression directly in the HepG2 hepatic cell line, thus leading to a decrease in intracellular Fe levels. Such inhibition was dependent on the Epo receptor-associated kinase JAK2, as well as on the PI3K/AKT/mTOR pathway, which regulates nutrient homeostasis. Epo was also found to decrease binding of the C/EBP-α transcription factor to the hepcidin promoter, which could be attributed to an increased expression of its inhibitor CHOP. Epo did not only hinder the stimulating effect of C/EBP-α on hepcidin transcription, but also favored hepcidin inhibition by HIF-1α, by increasing is nuclear translocation as well as its protein levels. Moreover, in assays with the inhibitor genistein, this transcription factor was found necessary for Epo-induced hepcidin suppression. Our findings support the involvement of the PI3K/AKT/mTOR pathway in the regulation of Fe levels by Epo, and highlight the contrasting roles of the C/EBP-α and HIF-1α transcription factors as downstream effectors of the cytokine in this process.

Erythroferrone in focus: emerging perspectives in iron metabolism and hematopathologies

Beyond its core role in iron metabolism, erythroferrone (ERFE) has emerged as a key player with far-reaching implications in various hematologic disorders. Its regulatory effect on hepcidin underlines its significance in conditions characterized by disrupted iron homeostasis. In β-thalassemia and myelodysplastic syndromes, its dysregulation intricately contributes to the clinical challenges of anemia and iron overload which highlights its potential as a therapeutic target. In anemia of chronic disease and iron deficiency anemia, ERFE presents a unique profile. In chronic kidney disease (CKD), the intricate interplay between ERFE, erythropoietin, and hepcidin undergoes dysregulation, contributing to the complex iron imbalance characteristic of this condition. Recent research suggests that ERFE plays a multifaceted role in restoring iron balance in CKD, beyond simply suppressing hepcidin production. The potential to modulate ERFE activity offers a novel approach to treating a spectrum of disorders associated with iron dysregulation. As our understanding of ERFE continues to evolve, it is poised to become a key focus in the development of targeted treatments, making it an exciting and dynamic area of ongoing research. Modulating ERFE activity presents a groundbreaking approach to treat iron dysregulation in conditions like iron deficiency anemia, thalassemia, and hemochromatosis. As new research unveils its intricate roles, ERFE has rapidly emerged as a key target for developing targeted therapies like ERFE agonists and antagonists. With promising studies underway, this dynamic field holds immense potential to improve patient outcomes, reduce complications, and offer personalized treatment options in hematology research. This comprehensive overview of ERFE's role across various conditions underscores its pivotal function in iron metabolism and associated pathologies.

Vamifeport: Monography of the First Oral Ferroportin Inhibitor

Over the last few years, several mechanisms that are involved in congenital diseases characterized by ineffective erythropoiesis have been described. Therefore, multiple new target drugs are being developed in preclinical models against the main regulators of normal erythropoiesis. Above all, the key mechanism that regulates systemic iron homeostasis, represented by the hepcidin-ferroportin axis, is considered to be the target for new therapies. The main hypothesis is that iron restriction, through blocking ferroportin (the unique iron transporter in mammals) in such diseases, ameliorates erythropoiesis. The action of vamifeport is different from the currently approved drugs in this setting since it acts straight on the ferroportin-hepcidin axis. The data presented in the sickle cell disease (SCD) Townes mouse model showed a preclinical proof-of-concept for the efficacy of oral ferroportin inhibitor. Vamifeport reduced hemoglobin concentration in red blood cells (RBCs) and diminished intravascular hemolysis and inflammation, improving hemodynamics and preventing vascular occlusive crises. On this basis, clinical trials were commenced in patients with SCD, non-transfusion-dependent (NTD) thalassemia and transfusion-dependent (TD) thalassemia. Preliminary data in NTD thalassemic patients also confirm the safety and efficacy in decreasing iron level. In conclusion, vamifeport represents a new option in the panorama of drugs targeting the hepcidin-ferroportin axis, but its efficacy is still under investigation as a single agent.

Acute blood loss in mice forces differentiation of both CD45-positive and CD45-negative erythroid cells and leads to a decreased CCL3 chemokine production by bone marrow erythroid cells

Hemorrhage, a condition that accompanies most physical trauma cases, remains an important field of study, a field that has been extensively studied in the immunological context for myeloid and lymphoid cells, but not as much for erythroid cells. In this study, we studied the immunological response of murine erythroid cells to acute blood loss using flow cytometry, NanoString immune transcriptome profiling, and BioPlex cytokine secretome profiling. We observed that acute blood loss forces the differentiation of murine erythroid cells in both bone marrow and spleen and that there was an up-regulation of several immune response genes, in particular pathogen-associated molecular pattern sensing gene Clec5a in post-acute blood loss murine bone marrow erythroid cells. We believe that the up-regulation of the Clec5a gene in bone marrow erythroid cells could help bone marrow erythroid cells detect and eliminate pathogens with the help of reactive oxygen species and antimicrobial proteins calprotectin and cathelicidin, the genes of which (S100a8, S100a9, and Camp) dominate the expression in bone marrow erythroid cells of mice.

Anemia and iron overload as prognostic markers of outcomes in β-thalassemia

INTRODUCTION

Ineffective erythropoiesis and subsequent anemia as well as primary and secondary (transfusional) iron overload are key drivers for morbidity and mortality outcomes in patients with β-thalassemia.

AREAS COVERED

In this review, we highlight evidence from observational studies evaluating the association between measures of anemia and iron overload versus outcomes in both non-transfusion-dependent and transfusion-dependent forms of β-thalassemia.

EXPERT OPINION

Several prognostic thresholds have been identified with implications for patient management. These have also formed the basis for the design of novel therapy clinical trials by informing eligibility and target endpoints. Still, several data gaps persist in view of the challenge of assessing prospective long-term outcomes in a chronic disease. Pooling insights on the prognostic value of different measures of disease mechanism will be key to design future scoring systems that can help optimize patient management.

Novel therapeutic approaches in thalassemias, sickle cell disease, and other red cell disorders

ABSTRACT

In this last decade, a deeper understanding of the pathophysiology of hereditary red cell disorders and the development of novel classes of pharmacologic agents have provided novel therapeutic approaches to thalassemias, sickle cell disease (SCD), and other red cell disorders. Here, we analyze and discuss the novel therapeutic options according to their targets, taking into consideration the complex process of erythroid differentiation, maturation, and survival of erythrocytes in the peripheral circulation. We focus on active clinical exploratory and confirmatory trials on thalassemias, SCD, and other red cell disorders. Beside β-thalassemia and SCD, we found that the development of new therapeutic strategies has allowed for the design of clinic studies for hereditary red cell disorders still lacking valuable therapeutic alternative such as α-thalassemias, congenital dyserythropoietic anemia, or Diamond-Blackfan anemia. In addition, reduction of heme synthesis, which can be achieved by the repurposed antipsychotic drug bitopertin, might affect not only hematological disorders but multiorgan diseases such as erythropoietic protoporphyria. Finally, our review highlights the current state of therapeutic scenarios, in which multiple indications targeting different red cell disorders are being considered for a single agent. This is a welcome change that will hopefully expand therapeutic option for patients affected by thalassemias, SCD, and other red cell disorders.

Key Genes FECH and ALAS2 under Acute High-Altitude Exposure: A Gene Expression and Network Analysis Based on Expression Profile Data

High-altitude acclimatization refers to the physiological adjustments and adaptation processes by which the human body gradually adapts to the hypoxic conditions of high altitudes after entering such environments. This study analyzed three mRNA expression profile datasets from the GEO database, focusing on 93 healthy residents from low altitudes (≤1400 m). Peripheral blood samples were collected for analysis on the third day after these individuals rapidly ascended to higher altitudes (3000-5300 m). The analysis identified significant differential expression in 382 genes, with 361 genes upregulated and 21 downregulated. Further, gene ontology (GO) annotation analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis indicated that the top-ranked enriched pathways are upregulated, involving blood gas transport, erythrocyte development and differentiation, and heme biosynthetic process. Network analysis highlighted ten key genes, namely, SLC4A1, FECH, EPB42, SNCA, GATA1, KLF1, GYPB, ALAS2, DMTN, and GYPA. Analysis revealed that two of these key genes, FECH and ALAS2, play a critical role in the heme biosynthetic process, which is pivotal in the development and maturation of red blood cells. These findings provide new insights into the key gene mechanisms of high-altitude acclimatization and identify potential biomarkers and targets for personalized acclimatization strategies.

Mitoxantrone ameliorates ineffective erythropoiesis in a β-thalassemia intermedia mouse model

ABSTRACT

β-thalassemia is a condition characterized by reduced or absent synthesis of β-globin resulting from genetic mutations, leading to expanded and ineffective erythropoiesis. Mitoxantrone has been widely used clinically as an antitumor agent considering its ability to inhibit cell proliferation. However, its therapeutic effect on expanded and ineffective erythropoiesis in β-thalassemia is untested. We found that mitoxantrone decreased α-globin precipitates and ameliorated anemia, splenomegaly, and ineffective erythropoiesis in the HbbTh3/+ mouse model of β-thalassemia intermedia. The partially reversed ineffective erythropoiesis is a consequence of effects on autophagy as mitochondrial retention and protein levels of mTOR, P62, and LC3 in reticulocytes decreased in mitoxantrone-treated HbbTh3/+ mice. These data provide significant preclinical evidence for targeting autophagy as a novel therapeutic approach for β-thalassemia.

Early erythroferrone levels can predict the long-term haemoglobin responses to erythropoiesis-stimulating agents

BACKGROUND AND PURPOSE

Our previous study reported that erythroferrone (ERFE), a newly identified hormone produced by erythroblasts, responded to recombinant human erythropoietin (rHuEPO) sensitively but its dynamics was complicated by double peaks and circadian rhythm. This study intends to elucidate the underlying mechanisms for the double peaks of ERFE dynamics and further determine whether early ERFE measurements can predict haemoglobin responses to rHuEPO.

EXPERIMENTAL APPROACH

By using the purified recombinant rat ERFE protein and investigating its deposition in rats, the production of ERFE was deconvoluted. To explore the role of iron in ERFE production, we monitored short-term changes of iron status after injection of rHuEPO or deferiprone. Pharmacokinetic/pharmacodynamic (PK/PD) modelling was used to confirm the mechanisms and examine the predictive ability of ERFE for long-term haemoglobin responses.

KEY RESULTS

The rRatERFE protein was successfully purified. The production of ERFE was deconvoluted and showed two independent peaks (2 and 8 h). Transient iron decrease was observed at 4 h after rHuEPO injection and deferiprone induced significant increases of ERFE. Based on this mechanism, the PK/PD model could characterize the complex dynamics of ERFE. In addition, the model predictions further revealed a stronger correlation between ERFE and haemoglobin peak values than that for observed values.

CONCLUSIONS AND IMPLICATIONS

The complex dynamics of ERFE should be composited by an immediate release and transient iron deficiency-mediated secondary production of ERFE. The early peak values of ERFE, which occur within a few hours, can predict haemoglobin responses several weeks after ESA treatment.

Effect of Single High-Dose Vitamin D3 Supplementation on Post-Ultra Mountain Running Heart Damage and Iron Metabolism Changes: A Double-Blind Randomized Controlled Trial

Exercise-induced inflammation can influence iron metabolism. Conversely, the effects of vitamin D3, which possesses anti-inflammatory properties, on ultramarathon-induced heart damage and changes in iron metabolism have not been investigated. Thirty-five healthy long-distance semi-amateur runners were divided into two groups: one group received 150,000 IU of vitamin D3 24 h prior to a race (n = 16), while the other group received a placebo (n = 19). Serum iron, hepcidin (HPC), ferritin (FER), erythroferrone (ERFE), erythropoietin (EPO), neopterin (NPT), and cardiac troponin T (cTnT) levels were assessed. A considerable effect of ultramarathon running on all examined biochemical markers was observed, with a significant rise in serum levels of ERFE, EPO, HPC, NPT, and cTnT detected immediately post-race, irrespective of the group factor. Vitamin D3 supplementation showed a notable interaction with the UM, specifically in EPO and cTnT, with no other additional changes in the other analysed markers. In addition to the correlation between baseline FER and post-run ERFE, HPC was modified by vitamin D. The ultramarathon significantly influenced the EPO/ERFE/HPC axis; however, a single substantial dose of vitamin D3 had an effect only on EPO, which was associated with the lower heart damage marker cTnT after the run.

Designing a single-arm phase 2 clinical trial of mitapivat for adult patients with erythrocyte membranopathies (SATISFY): a framework for interventional trials in rare anaemias - pilot study protocol

INTRODUCTION

Membranopathies encompass haemolytic disorders arising from genetic variants in erythrocyte membrane proteins, including hereditary spherocytosis and stomatocytosis. Congenital dyserythropoietic anaemia type II (CDA II) is associated with the SEC23B gene and can exhibit phenotypic similarities to membranopathies. Current treatment options for these conditions, apart from splenectomy, are primarily supportive. Mitapivat, a novel pyruvate kinase (PK) activator, has demonstrated efficacy in increasing haemoglobin levels and reducing haemolysis in patients with PK deficiency, thalassemia, sickle cell disease and a mouse model of hereditary spherocytosis.

METHODS AND ANALYSES

Safety and efficacy of mitapivat sulfate in adult patients with erythrocyte membranopathies (SATISFY) is a prospective, multicentre, single-arm phase two trial involving approximately 25 adult patients (≥18 years) diagnosed with a membranopathy or CDA II. During the 8-week dose escalation period, subjects will receive an initial dose of 50 mg mitapivat two times per day and may increase to 100 mg two times per day at week 4 based on the safety and changes in haemoglobin levels. Patients tolerating mitapivat well may be eligible to continue in two consecutive 24-week fixed dose periods.The primary objective of this study is to evaluate the safety of mitapivat, assessed through the occurrence of treatment-emergent adverse events. Secondary objectives include assessing the effects of mitapivat on haemoglobin levels, haemolysis, erythropoiesis, patient-reported outcome measures and spleen size.SATISFY aims to assess the safety and efficacy of mitapivat in adult patients with red blood cell membranopathies and CDA II, with the aim of establishing proof-of-concept in patients living with these rare conditions.

ETHICS AND DISSEMINATION

NCT05935202/CTIS:2023-503271-24-01. Findings will be published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

Clinicaltrials.gov, NCT05935202. CTIS:2023-503271-24-01. Registered 07-July-2023. Protocol number: 2.1. https://clinicaltrials.gov/study/NCT05935202.

Research progress on high-concentration oxygen therapy after cerebral hemorrhage

Recently, the role of high-concentration oxygen therapy in cerebral hemorrhage has been extensively discussed. This review describes the research progress in high-concentration oxygen therapy after cerebral hemorrhage. High-concentration oxygen therapy can be classified into two treatment methods: hyperbaric and normobaric high-concentration oxygen therapy. Several studies have reported that high-concentration oxygen therapy uses the pathological mechanisms of secondary ischemia and hypoxia after cerebral hemorrhage as an entry point to improve cerebral oxygenation, metabolic rate, cerebral edema, intracranial pressure, and oxidative stress. We also elucidate the mechanisms by which molecules such as Hypoxia-inducible factor 1-alpha (HIF-1α), vascular endothelial growth factor, and erythropoietin (EPO) may play a role in oxygen therapy. Although people are concerned about the toxicity of hyperoxia, combined with relevant literature, the evidence discussed in this article suggests that as long as the duration, concentration, pressure, and treatment interval of patients with cerebral hemorrhage are properly understood and oxygen is administered within the treatment window, it can be effective to avoid hyperoxic oxygen toxicity. Combined with the latest research, we believe that high-concentration oxygen therapy plays an important positive role in injuries and outcomes after cerebral hemorrhage, and we recommend expanding the use of normal-pressure high-concentration oxygen therapy for cerebral hemorrhage.

Genetic Determined Iron Starvation Signature in Friedreich's Ataxia

BACKGROUND

Early studies in cellular models suggested an iron accumulation in Friedreich's ataxia (FA), yet findings from patients are lacking.

OBJECTIVES

The objective is to characterize systemic iron metabolism, body iron storages, and intracellular iron regulation in FA patients.

METHODS

In FA patients and matched healthy controls, we assessed serum iron parameters, regulatory hormones as well as the expression of regulatory proteins and iron distribution in peripheral blood mononuclear cells (PBMCs). We applied magnetic resonance imaging with R2*-relaxometry to quantify iron storages in the liver, spleen, and pancreas. Across all evaluations, we assessed the influence of the genetic severity as expressed by the length of the shorter GAA-expansion (GAA1).

RESULTS

We recruited 40 FA patients (19 women). Compared to controls, FA patients displayed lower serum iron and transferrin saturation. Serum ferritin, hepcidin, mean corpuscular hemoglobin and mean corpuscular volume in FA inversely correlated with the GAA1-repeat length, indicating iron deficiency and restricted availability for erythropoiesis with increasing genetic severity. R2*-relaxometry revealed a reduction of splenic and hepatic iron stores in FA. Liver and spleen R2* values inversely correlated with the GAA1-repeat length. FA PBMCs displayed downregulation of ferritin and upregulation of transferrin receptor and divalent metal transporter-1 mRNA, particularly in patients with >500 GAA1-repeats. In FA PBMCs, intracellular iron was not increased, but shifted toward mitochondria.

CONCLUSIONS

We provide evidence for a previously unrecognized iron starvation signature at systemic and cellular levels in FA patients, which is related to the underlying genetic severity. These findings challenge the use of systemic iron lowering therapies in FA. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Combination of a TGF-β ligand trap (RAP-GRL) and TMPRSS6-ASO is superior for correcting β-thalassemia

A recently approved drug that induces erythroid cell maturation (luspatercept) has been shown to improve anemia and reduce the need for blood transfusion in non-transfusion-dependent as well as transfusion-dependent β-thalassemia (BT) patients. Although these results were predominantly positive, not all the patients showed the expected increase in hemoglobin (Hb) levels or transfusion burden reduction. Additional studies indicated that administration of luspatercept in transfusion-dependent BT was associated with increased erythropoietic markers, decreased hepcidin levels, and increased liver iron content. Altogether, these studies suggest that luspatercept may necessitate additional drugs for improved erythroid and iron management. As luspatercept does not appear to directly affect iron metabolism, we hypothesized that TMPRSS6-ASO could improve iron parameters and iron overload when co-administered with luspatercept. We used an agent analogous to murine luspatercept (RAP-GRL) and another novel therapeutic, IONIS TMPRSS6-LRx (TMPRSS6-ASO), a hepcidin inducer, to treat non-transfusion-dependent BT-intermedia mice. Our study shows that RAP-GRL alone improved red blood cell (RBC) production, with no or limited effect on splenomegaly and iron parameters. In contrast, TMPRSS6-ASO improved RBC measurements, ameliorated splenomegaly, and improved iron overload most effectively. Our results provide pre-clinical support for combining TMPRSS6-ASO and luspatercept in treating BT, as these drugs together show potential for simultaneously improving both erythroid and iron parameters in BT patients.

Fibrinogen-like 1: A hepatokine linking liver physiology to hematology

A recent study identified the critical contribution of the hepatokine FGL1 to the regulation of iron metabolism during the recovery from anemia. FGL1 is secreted by hepatocytes in response to hypoxia to sequester BMP ligands and repress the transcription of the iron-regulatory hormone hepcidin. This process ensures the proper supply of iron to the bone marrow for new red blood cell synthesis and the restoration of physiological oxygen levels. FGL1 may therefore contribute to the recovery from common anemias and cause iron overload in chronic anemias with ineffective erythropoiesis, such as ß-thalassemia, dyserythropoietic anemia, and myelodysplastic syndromes. However, FGL1 has also been described as a regulator of hepatocyte proliferation, glucose homeostasis, and insulin signaling, as well as a mediator of liver steatosis and immune evasion. Chronic exposure to elevated levels of FGL1 during anemia may therefore have systemic metabolic effects besides iron regulation and erythropoiesis. Here, we are providing an overview of the proposed functions of FGL1 in physiology and pathophysiology.

Advances of Iron and Ferroptosis in Diabetic Kidney Disease

Diabetes mellitus presents a significant threat to human health because it disrupts energy metabolism and gives rise to various complications, including diabetic kidney disease (DKD). Metabolic adaptations occurring in the kidney in response to diabetes contribute to the pathogenesis of DKD. Iron metabolism and ferroptosis, a recently defined form of cell death resulting from iron-dependent excessive accumulation of lipid peroxides, have emerged as crucial players in the progression of DKD. In this comprehensive review, we highlight the profound impact of adaptive and maladaptive responses regulating iron metabolism on the progression of kidney damage in diabetes. We summarize the current understanding of iron homeostasis and ferroptosis in DKD. Finally, we propose that precise manipulation of iron metabolism and ferroptosis may serve as potential strategies for kidney management in diabetes.

Bone marrow Tfr2 deletion improves the therapeutic efficacy of the activin-receptor ligand trap RAP-536 in β-thalassemic mice

β-thalassemia is a disorder characterized by anemia, ineffective erythropoiesis (IE), and iron overload, whose treatment still requires improvement. The activin receptor-ligand trap Luspatercept, a novel therapeutic option for β-thalassemia, stimulates erythroid differentiation inhibiting the transforming growth factor β pathway. However, its exact mechanism of action and the possible connection with erythropoietin (Epo), the erythropoiesis governing cytokine, remain to be clarified. Moreover, Luspatercept does not correct all the features of the disease, calling for the identification of strategies that enhance its efficacy. Transferrin receptor 2 (TFR2) regulates systemic iron homeostasis in the liver and modulates the response to Epo of erythroid cells, thus balancing red blood cells production with iron availability. Stimulating Epo signaling, hematopoietic Tfr2 deletion ameliorates anemia and IE in Hbbth3/+ thalassemic mice. To investigate whether hematopoietic Tfr2 inactivation improves the efficacy of Luspatercept, we treated Hbbth3/+ mice with or without hematopoietic Tfr2 (Tfr2BMKO/Hbbth3/+) with RAP-536, the murine analog of Luspatercept. As expected, both hematopoietic Tfr2 deletion and RAP-536 significantly ameliorate IE and anemia, and the combined approach has an additive effect. Since RAP-536 has comparable efficacy in both Hbbth3/+ and Tfr2BMKO/Hbbth3/+ animals, we propose that the drug promotes erythroid differentiation independently of TFR2 and EPO stimulation. Notably, the lack of Tfr2, but not RAP-536, can also attenuate iron-overload and related complications. Overall, our results shed further light on the mechanism of action of Luspatercept and suggest that strategies aimed at inhibiting hematopoietic TFR2 might improve the therapeutic efficacy of activin receptor-ligand traps.

Iron deficiency and supplementation in heart failure

Non-anaemic iron deficiency (NAID) is a strategic target in cardiovascular medicine because of its association with a range of adverse effects in various conditions. Endeavours to tackle NAID in heart failure have yielded mixed results, exposing knowledge gaps in how best to define 'iron deficiency' and the handling of iron therapies by the body. To address these gaps, we harness the latest understanding of the mechanisms of iron homeostasis outside the erythron and integrate clinical and preclinical lines of evidence. The emerging picture is that current definitions of iron deficiency do not assimilate the multiple influences at play in patients with heart failure and, consequently, fail to identify those with a truly unmet need for iron. Additionally, current iron supplementation therapies benefit only certain patients with heart failure, reflecting differences in the nature of the unmet need for iron and the modifying effects of anaemia and inflammation on the handling of iron therapies by the body. Building on these insights, we identify untapped opportunities in the management of NAID, including the refinement of current approaches and the development of novel strategies. Lessons learned from NAID in cardiovascular disease could ultimately translate into benefits for patients with other chronic conditions such as chronic kidney disease, chronic obstructive pulmonary disease and cancer.

The drug-specific properties of hypoxia-inducible factor-prolyl hydroxylase inhibitors in mice reveal a significant contribution of the kidney compared to the liver to erythropoietin induction

AIMS

Kidney disease often leads to anemia due to a defect in the renal production of the erythroid growth factor erythropoietin (EPO), which is produced under the positive regulation of hypoxia-inducible transcription factors (HIFs). Chemical compounds that inhibit HIF-prolyl hydroxylases (HIF-PHs), which suppress HIFs, have been developed to reactivate renal EPO production in renal anemia patients. Currently, multiple HIF-PH inhibitors, in addition to conventional recombinant EPO reagents, are used for renal anemia treatment. This study aimed to elucidate the therapeutic mechanisms and drug-specific properties of HIF-PH inhibitors.

METHODS AND KEY FINDINGS

Gene expression analyses and mass spectrometry revealed that HIF-PH inhibitors (daprodustat, enarodustat, molidustat, and vadadustat) alter Epo gene expression levels in the kidney and liver in a drug-specific manner, with different pharmacokinetics in the plasma and urine after oral administration to mice. The drug specificity revealed the dominant contribution of EPO induction in the kidneys rather than in the liver to plasma EPO levels after HIF-PH inhibitor administration. We also found that several HIF-PH inhibitors directly induce duodenal gene expression related to iron intake, while these drugs indirectly suppress hepatic hepcidin expression to mobilize stored iron for hemoglobin synthesis through induction of the EPO-erythroferrone axis.

SIGNIFICANCE

Renal EPO induction is the major target of HIF-PH inhibitors for their therapeutic effects on erythropoiesis. Additionally, the drug-specific properties of HIF-PH inhibitors in EPO induction and iron metabolism have been shown in mice, providing useful information for selecting the proper HIF-PH inhibitor for each renal anemia patient.

Mitapivat improves ineffective erythropoiesis and iron overload in adult patients with pyruvate kinase deficiency

ABSTRACT

Pyruvate kinase (PK) deficiency is a rare, hereditary disease characterized by chronic hemolytic anemia. Iron overload is a common complication regardless of age, genotype, or transfusion history. Mitapivat, an oral, allosteric PK activator, improves anemia and hemolysis in adult patients with PK deficiency. Mitapivat's impact on iron overload and ineffective erythropoiesis was evaluated in adults with PK deficiency who were not regularly transfused in the phase 3 ACTIVATE trial and long-term extension (LTE) (#NCT03548220/#NCT03853798). Patients in the LTE received mitapivat throughout ACTIVATE/LTE (baseline to week 96; mitapivat-to-mitapivat [M/M] arm) or switched from placebo (baseline to week 24) to mitapivat (week 24 to week 96; placebo-to-mitapivat [P/M] arm). Changes from baseline in markers of iron overload and erythropoiesis were assessed to week 96. Improvements in hepcidin (mean, 4770.0 ng/L; 95% confidence interval [CI], -1532.3 to 11 072.3), erythroferrone (mean, -9834.9 ng/L; 95% CI, -14 328.4 to -5341.3), soluble transferrin receptor (mean, -56.0 nmol/L; 95% CI, -84.8 to -27.2), and erythropoietin (mean, -32.85 IU/L; 95% CI, -54.65 to -11.06) were observed in the M/M arm (n = 40) from baseline to week 24, sustained to week 96. No improvements were observed in the P/M arm (n = 40) to week 24; however, upon transitioning to mitapivat, improvements similar to those observed in the M/M arm were seen. Mean changes from baseline in liver iron concentration by magnetic resonance imaging at week 96 in the M/M arm and the P/M arm were -2.0 mg Fe/g dry weight (dw; 95% CI, -4.8 to -0.8) and -1.8 mg Fe/g dw (95% CI, -4.4 to 0.80), respectively. Mitapivat is the first disease-modifying pharmacotherapy shown to have beneficial effects on iron overload and ineffective erythropoiesis in patients with PK deficiency. This trial was registered at www.ClinicalTrials.gov as #NCT03548220 (ACTIVATE) and #NCT03853798 (LTE).

Understanding iron homeostasis in MDS: the role of erythroferrone

Myelodysplastic neoplasms (MDS) are a heterogenous group of clonal stem cell disorders characterized by dysplasia and cytopenia in one or more cell lineages. Anemia is a very common symptom that is often treated with blood transfusions and/or erythropoiesis stimulating factors. Iron overload results from a combination of these factors together with the disease-associated ineffective erythropoiesis, that is seen especially in MDS cases with SF3B1 mutations. A growing body of research has shown that erythroferrone is an important regulator of hepcidin, the master regulator of systemic iron homeostasis. Consequently, it is of interest to understand how this molecule contributes to regulating the iron balance in MDS patients. This short review evaluates our current understanding of erythroferrone in general, but more specifically in MDS and seeks to place in context how the current knowledge could be utilized for prognostication and therapy.

TFPI from erythroblasts drives heme production in central macrophages promoting erythropoiesis in polycythemia

Bleeding and thrombosis are known as common complications of polycythemia for a long time. However, the role of coagulation system in erythropoiesis is unclear. Here, we discover that an anticoagulant protein tissue factor pathway inhibitor (TFPI) plays an essential role in erythropoiesis via the control of heme biosynthesis in central macrophages. TFPI levels are elevated in erythroblasts of human erythroblastic islands with JAK2V617F mutation and hypoxia condition. Erythroid lineage-specific knockout TFPI results in impaired erythropoiesis through decreasing ferrochelatase expression and heme biosynthesis in central macrophages. Mechanistically, the TFPI interacts with thrombomodulin to promote the downstream ERK1/2-GATA1 signaling pathway to induce heme biosynthesis in central macrophages. Furthermore, TFPI blockade impairs human erythropoiesis in vitro, and normalizes the erythroid compartment in mice with polycythemia. These results show that erythroblast-derived TFPI plays an important role in the regulation of erythropoiesis and reveal an interplay between erythroblasts and central macrophages.

Crosstalk between oxygen signaling and iron metabolism in renal interstitial fibroblasts

To maintain the oxygen supply, the production of red blood cells (erythrocytes) is promoted under low-oxygen conditions (hypoxia). Oxygen is carried by hemoglobin in erythrocytes, in which the majority of the essential element iron in the body is contained. Because iron metabolism is strictly controlled in a semi-closed recycling system to protect cells from oxidative stress caused by iron, hypoxia-inducible erythropoiesis is closely coordinated by regulatory systems that mobilize stored iron for hemoglobin synthesis. The erythroid growth factor erythropoietin (EPO) is mainly secreted by interstitial fibroblasts in the renal cortex, which are known as renal EPO-producing (REP) cells, and promotes erythropoiesis and iron mobilization. Intriguingly, EPO production is strongly induced by hypoxia through iron-dependent pathways in REP cells. Here, we summarize recent studies on the network mechanisms linking hypoxia-inducible EPO production, erythropoiesis and iron metabolism. Additionally, we introduce disease mechanisms related to disorders in the network mediated by REP cell functions. Furthermore, we propose future studies regarding the application of renal cells derived from the urine of kidney disease patients to investigate the molecular pathology of chronic kidney disease and develop precise and personalized medicine for kidney disease.

Anemia in Pregnancy With CKD

Chronic kidney disease (CKD), anemia, and iron deficiency are global health issues affecting individuals in both high-income and low-income countries. In pregnancy, both CKD and iron deficiency anemia increase the risk of adverse maternal and neonatal outcomes, including increased maternal morbidity and mortality, stillbirth, perinatal death, preterm birth, and low birthweight. However, it is unknown to which extent iron deficiency anemia contributes to adverse outcomes in CKD pregnancy. Furthermore, little is known regarding the prevalence, pathophysiology, and treatment of iron deficiency and anemia in pregnant women with CKD. Therefore, there are many unanswered questions regarding optimal management with oral or i.v. iron and recombinant human erythropoietin (rhEPO) in these women. In this review, we present a short overview of the (patho)physiology of anemia in healthy pregnancy and in people living with CKD. We present an evaluation of the literature on iron deficiency, anemia, and nutritional deficits in pregnant women with CKD; and we evaluate current knowledge gaps. Finally, we propose research priorities regarding anemia in pregnant women with CKD.

Non-Classical Effects of FGF23: Molecular and Clinical Features

This article reviews the role of fibroblast growth factor 23 (FGF23) protein in phosphate metabolism, highlighting its regulation of vitamin D, parathyroid hormone, and bone metabolism. Although it was traditionally thought that phosphate-calcium homeostasis was controlled exclusively by parathyroid hormone (PTH) and calcitriol, pathophysiological studies revealed the influence of FGF23. This protein, expressed mainly in bone, inhibits the renal reabsorption of phosphate and calcitriol formation, mediated by the α-klotho co-receptor. In addition to its role in phosphate metabolism, FGF23 exhibits pleiotropic effects in non-renal systems such as the cardiovascular, immune, and metabolic systems, including the regulation of gene expression and cardiac fibrosis. Although it has been proposed as a biomarker and therapeutic target, the inhibition of FGF23 poses challenges due to its potential side effects. However, the approval of drugs such as burosumab represents a milestone in the treatment of FGF23-related diseases.

A Revised Classification of Primary Iron Overload Syndromes

Background and Aims

The clinical introduction of hepcidin25 (Hep25) has led to a more detailed understanding of its relationship with ferroportin (FP) and divalent metal transporter1 in primary iron overload syndromes (PIOSs). In 2012, we proposed a classification of PIOSs based on the Hep25/FP system, which consists of prehepatic aceruloplasminemia, hepatic hemochromatosis (HC), and posthepatic FP disease (FP-D). However, in consideration of accumulated evidence on PIOSs, we aimed to renew the classification.

Methods

We reviewed the 2012 classification and retrospectively renewed it according to new information on PIOSs.

Results

Iron-loading anemia was included in PIOSs as a prehepatic form because of the newly discovered erythroferrone-induced suppression of Hep25, and the state of traditional FP-D was remodeled as the BIOIRON proposal. The key molecules responsible for prehepatic PIOSs are low transferrin saturation in aceruloplasminemia and increased erythroferrone production by erythroblasts in iron-loading anemia. Hepatic PIOSs comprise four genotypes of HC, in each of which the synthesis of Hep25 is inappropriately reduced in the liver. Hepatic Hep25 synthesis is adequate in posthepatic PIOSs; however, two mutant FP molecules may resist Hep25 differently, resulting in SLC40A1-HC and FP-D, respectively. PIOS phenotypes are diagnosed using laboratory tests, including circulating Hep25, followed by suitable treatments. Direct sequencing of the candidate genes may be outsourced to gene centers when needed. Laboratory kits for the prevalent mutations, such as C282Y, may be the first choice for a genetic analysis of HC in Caucasians.

Conclusions

The revised classification may be useful worldwide.

A human anti-matriptase-2 antibody limits iron overload, α-globin aggregates, and splenomegaly in β-thalassemic mice

ABSTRACT

Iron plays a major role in the deterioration of β-thalassemia. Indeed, the high levels of transferrin saturation and iron delivered to erythroid progenitors are associated with production of α-globin precipitates that negatively affect erythropoiesis. Matriptase-2/TMPRSS6, a membrane-bound serine protease expressed in hepatocytes, negatively modulates hepcidin production and thus is a key target to prevent iron overload in β-thalassemia. To address safety concerns raised by the suppression of Tmprss6 by antisense oligonucleotides or small interfering RNA, we tested a fully human anti-matriptase-2 antibody, RLYB331, which blocks the protease activity of matriptase-2. When administered weekly to Hbbth3/+ mice, RLYB331 induced hepcidin expression, reduced iron loading, prevented the formation of toxic α-chain/heme aggregates, reduced ros oxygen species formation, and improved reticulocytosis and splenomegaly. To increase the effectiveness of RLYB331 in β-thalassemia treatment even further, we administered RLYB331 in combination with RAP-536L, a ligand-trapping protein that contains the extracellular domain of activin receptor type IIB and alleviates anemia by promoting differentiation of late-stage erythroid precursors. RAP-536L alone did not prevent iron overload but significantly reduced apoptosis in the erythroid populations of the bone marrow, normalized red blood cell counts, and improved hemoglobin and hematocrit levels. Interestingly, the association of RLYB331 with RAP-536L entirely reversed the β-thalassemia phenotype in Hbbth3/+ mice and simultaneously corrected iron overload, ineffective erythropoiesis, splenomegaly, and hematological parameters, suggesting that a multifunctional molecule consisting of the fusion of RLYB331 with luspatercept (human version of RAP-536L) would allow administration of a single medication addressing simultaneously the different pathophysiological aspects of β-thalassemia.

Iron Absorption: Molecular and Pathophysiological Aspects

Iron is an essential nutrient for growth among all branches of life, but while iron is among the most common elements, bioavailable iron is a relatively scarce nutrient. Since iron is fundamental for several biological processes, iron deficiency can be deleterious. On the other hand, excess iron may lead to cell and tissue damage. Consequently, iron balance is strictly regulated. As iron excretion is not physiologically controlled, systemic iron homeostasis is maintained at the level of absorption, which is mainly influenced by the amount of iron stores and the level of erythropoietic activity, the major iron consumer. Here, we outline recent advances that increased our understanding of the molecular aspects of iron absorption. Moreover, we examine the impact of these recent insights on dietary strategies for maintaining iron balance.

Nrf2 Plays a Key Role in Erythropoiesis during Aging

Aging is characterized by increased oxidation and reduced efficiency of cytoprotective mechanisms. Nuclear factor erythroid-2-related factor (Nrf2) is a key transcription factor, controlling the expression of multiple antioxidant proteins. Here, we show that Nrf2-/- mice displayed an age-dependent anemia, due to the combined contributions of reduced red cell lifespan and ineffective erythropoiesis, suggesting a role of Nrf2 in erythroid biology during aging. Mechanistically, we found that the expression of antioxidants during aging is mediated by activation of Nrf2 function by peroxiredoxin-2. The absence of Nrf2 resulted in persistent oxidation and overactivation of adaptive systems such as the unfolded protein response (UPR) system and autophagy in Nrf2-/- mouse erythroblasts. As Nrf2 is involved in the expression of autophagy-related proteins such as autophagy-related protein (Atg) 4-5 and p62, we found impairment of late phase of autophagy in Nrf2-/- mouse erythroblasts. The overactivation of the UPR system and impaired autophagy drove apoptosis of Nrf2-/- mouse erythroblasts via caspase-3 activation. As a proof of concept for the role of oxidation, we treated Nrf2-/- mice with astaxanthin, an antioxidant, in the form of poly (lactic-co-glycolic acid) (PLGA)-loaded nanoparticles (ATS-NPs) to improve its bioavailability. ATS-NPs ameliorated the age-dependent anemia and decreased ineffective erythropoiesis in Nrf2-/- mice. In summary, we propose that Nrf2 plays a key role in limiting age-related oxidation, ensuring erythroid maturation and growth during aging.

Erythroferrone and hepcidin levels in children with iron deficiency anemia

BACKGROUND

Iron deficiency anemia remains a significant public health issue in developing countries. The regulation of iron metabolism is primarily controlled by hepcidin, a key regulatory protein. During erythropoiesis, erythroferrone (ERFE), a hormone produced by erythroblasts in response to erythropoietin (EPO) synthesis, mediates the suppression of hepcidin. In this study, it was aimed to determine the correlation between erythroferrone (ERFE) and hepcidin levels in children with iron deficiency anemia.

METHODS

This is a case-control study conducted at Kırşehir Ahi Evran University Training and Research Hospital Pediatrics Clinic between 1 and 31 September 2020. The study included 26 healthy children and 26 children with iron deficiency anemia. In order to evaluate iron status,whole blood count, serum iron, total iron binding capacity (TIBC), and ferritin levels were analyzed. The study measured the levels of hepcidin and erythroferrone in the serum of children diagnosed with iron deficiency before and after one month of iron treatment, as well as in a control group, using the ELISA method. Correlation between whole blood count, initial ferritin, hepcidin, ERFE and ferritin in the iron deficiency group was evaluated.

RESULTS

Compared with healthy controls, the iron-deficient group had significantly lower haemoglobin (p < 0.001), MCV (p = 0.001), MCH (p < 0.001), MCHC (p < 0.001), iron (p < 0.001), ferritin (p < 0.001) and hepcidin (p = 0.001). Ferritin and hepcidin levels increased while erythroferrone levels remained unchanged after iron deficiency treatment. There was no correlation between hepcidin and ferritin levels in treatment group.

CONCLUSIONS

The study found a strong and positive correlation between ferritin and hepcidin levels in iron-deficient children, but not between ERFE levels, suggesting that hepcidin is largely regulated by iron deposition levels. In addition, there was an increase in ferritin and hepcidin levels after iron treatment. The study found no significant difference in erythroferrone levels between the iron-deficient group and the control group. It is thought that this may be due to the short duration of iron treatment given to the patients with iron deficiency anemia included in the study.

Iron, Copper, and Selenium: Cancer's Thing for Redox Bling

Cells require micronutrients for numerous basic functions. Among these, iron, copper, and selenium are particularly critical for redox metabolism, and their importance is heightened during oncogene-driven perturbations in cancer. In this review, which particularly focuses on iron, we describe how these micronutrients are carefully chaperoned about the body and made available to tissues, a process that is designed to limit the toxicity of free iron and copper or by-products of selenium metabolism. We delineate perturbations in iron metabolism and iron-dependent proteins that are observed in cancer, and describe the current approaches being used to target iron metabolism and iron-dependent processes.

Measurement of serum hepcidin-25 by latex agglutination in healthy volunteers and patients with hematologic disorders

Iron is an essential trace metal, vital for various physiologic processes, but excess levels can harm health. Maintaining iron homeostasis is critical, with hepcidin playing a key role. The isoform hepcidin-25 exerts the most significant influence on iron metabolism, making its serum levels a valuable diagnostic tool. However, mass-spectrometry and other conventional measurement methods can be difficult to perform, and some immunoassays lack reliability. In this study, we employed a recently developed latex agglutination method integrated with a readily available automated analyzer to quantify serum hepcidin-25 levels in both volunteers recruited from personnel of our hospital (n = 93) and patients with various hematological disorders (n = 112). Our findings unveiled a robust positive correlation between serum hepcidin-25 and ferritin, as well as C-reactive protein levels, in both volunteers and patients. Among the patients with hematological disorders, there was a noteworthy negative correlation between hepcidin-25 levels and hemoglobin concentrations, as well as reticulocyte counts. Interestingly, the hepcidin-25/ferritin ratio was remarkably low in patients with hemolytic anemia and myelodysplastic syndromes with ring sideroblasts. Our findings suggest that quantifying serum hepcidin-25 and the hepcidin-25/ferritin ratio using this method may be valuable for screening of hematopoietic diseases and other iron metabolism disorders.

The hepatokine FGL1 regulates hepcidin and iron metabolism during anemia in mice by antagonizing BMP signaling

ABSTRACT

As a functional component of erythrocyte hemoglobin, iron is essential for oxygen delivery to all tissues in the body. The liver-derived peptide hepcidin is the master regulator of iron homeostasis. During anemia, the erythroid hormone erythroferrone regulates hepcidin synthesis to ensure the adequate supply of iron to the bone marrow for red blood cell production. However, mounting evidence suggested that another factor may exert a similar function. We identified the hepatokine fibrinogen-like 1 (FGL1) as a previously undescribed suppressor of hepcidin that is induced in the liver in response to hypoxia during the recovery from anemia, and in thalassemic mice. We demonstrated that FGL1 is a potent suppressor of hepcidin in vitro and in vivo. Deletion of Fgl1 in mice results in higher hepcidin levels at baseline and after bleeding. FGL1 exerts its activity by directly binding to bone morphogenetic protein 6 (BMP6), thereby inhibiting the canonical BMP-SMAD signaling cascade that controls hepcidin transcription.

Iron Metabolism and Inflammatory Mediators in Patients with Renal Dysfunction

Chronic kidney disease (CKD) affects around 850 million people worldwide, posing significant challenges in healthcare due to complications like renal anemia, end-stage kidney disease, and cardiovascular diseases. This review focuses on the intricate interplay between iron metabolism, inflammation, and renal dysfunction in CKD. Renal anemia, prevalent in CKD, arises primarily from diminished erythropoietin (EPO) production and iron dysregulation, which worsens with disease progression. Functional and absolute iron deficiencies due to impaired absorption and chronic inflammation are key factors exacerbating erythropoiesis. A notable aspect of CKD is the accumulation of uremic toxins, such as indoxyl sulfate (IS), which hinder iron metabolism and worsen anemia. These toxins directly affect renal EPO synthesis and contribute to renal hypoxia, thus playing a critical role in the pathophysiology of renal anemia. Inflammatory cytokines, especially TNF-α and IL-6, further exacerbate CKD progression and disrupt iron homeostasis, thereby influencing anemia severity. Treatment approaches have evolved to address both iron and EPO deficiencies, with emerging therapies targeting hepcidin and employing hypoxia-inducible factor (HIF) stabilizers showing potential. This review underscores the importance of integrated treatment strategies in CKD, focusing on the complex relationship between iron metabolism, inflammation, and renal dysfunction to improve patient outcomes.

Activation of Intestinal HIF2α Ameliorates Iron-Refractory Anemia

In clinics, hepcidin levels are elevated in various anemia-related conditions, particularly in iron-refractory anemia and in high inflammatory states that suppress iron absorption, which remains an urgent unmet medical need. To identify effective treatment options for various types of iron-refractory anemia, the potential effect of hypoxia and pharmacologically-mimetic drug FG-4592 (Roxadustat) are evaluated, a hypoxia-inducible factor (HIF)-prolyl hydroxylase (PHD) inhibitor, on mouse models of iron-refractory iron-deficiency anemia (IRIDA), anemia of inflammation and 5-fluorouracil-induced chemotherapy-related anemia. The potent protective effects of both hypoxia and FG-4592 on IRIDA as well as other 2 tested mouse cohorts are found. Mechanistically, it is demonstrated that hypoxia or FG-4592 could stabilize duodenal Hif2α, leading to the activation of Fpn transcription regardless of hepcidin levels, which in turn results in increased intestinal iron absorption and the amelioration of hepcidin-activated anemias. Moreover, duodenal Hif2α overexpression fully rescues phenotypes of Tmprss6 knockout mice, and Hif2α knockout in the gut significantly delays the recovery from 5-fluorouracil-induced anemia, which can not be rescued by FG-4592 treatment. Taken together, the findings of this study provide compelling evidence that targeting intestinal hypoxia-related pathways can serve as a potential therapeutic strategy for treating a broad spectrum of anemia, especially iron refractory anemia.

Oral iron therapy: Current concepts and future prospects for improving efficacy and outcomes

Iron deficiency (ID) and iron-deficiency anaemia (IDA) are global public health concerns, most commonly afflicting children, pregnant women and women of childbearing age. Pathological outcomes of ID include delayed cognitive development in children, adverse pregnancy outcomes and decreased work capacity in adults. IDA is usually treated by oral iron supplementation, typically using iron salts (e.g. FeSO4 ); however, dosing at several-fold above the RDA may be required due to less efficient absorption. Excess enteral iron causes adverse gastrointestinal side effects, thus reducing compliance, and negatively impacts the gut microbiome. Recent research has sought to identify new iron formulations with better absorption so that lower effective dosing can be utilized. This article outlines emerging research on oral iron supplementation and focuses on molecular mechanisms by which different supplemental forms of iron are transported across the intestinal epithelium and whether these transport pathways are subject to regulation by the iron-regulatory hormone hepcidin.