Management of iron overload: lessons from transfusion-dependent hemoglobinopathies

ABSTRACT

Before the advent of effective iron chelation, death from iron-induced cardiomyopathy and endocrine failure occurred in the second decade in patients with thalassemia major, and this experience has driven expectation of poor outcomes and caused anxiety in all disorders associated with iron loading to this day. To be clear, severe iron overload still causes significant morbidity and mortality in many parts of the world, but current understanding of iron metabolism, noninvasive monitoring of organ-specific iron loading in humans, and effective iron chelators have dramatically reduced morbidity of iron overload. Furthermore, clinical experience in hemoglobinopathies supports iron biology learned from animal studies and identifies common concepts in the biology of iron toxicity that inform the management of iron toxicity in several human disorders. The resultant significant increase in survival uncovers new complications due to much longer exposure to anemia and to iron, which must be considered in long-term therapeutic strategies. This review will discuss the management of iron toxicity in patients with hemoglobinopathies and transfusion-dependent anemias and how iron biology informs the clinical approach to treatment.

Transfusional hemosiderosis in childhood cancer patients and survivors

BACKGROUND

Children treated for cancer are at risk for adverse effects of iron due to transfusions administered during prolonged marrow suppression, which may increase exposure to toxic forms of iron, extrahepatic iron accumulation, and long-term organ damage.

OBJECTIVE

This study aimed to characterize the severity and organ distribution of clinically significant, multisystem iron overload (IO) in an at-risk cohort of pediatric cancer patients.

METHODS

This was a retrospective, cross-sectional study of childhood cancer patients who underwent a magnetic resonance imaging (MRI) due to clinical concern for IO. Data regarding cancer type and treatment, transfusion history, MRI and laboratory results, and treatment for IO were collected. Severity of IO was analyzed by non-parametric tests with respect to clinical characteristics.

RESULTS

Of the 103 patients, 98% of whom had a Cancer Intensity Treatment Rating (ITR-3) of 3 or higher, 53% (54/102) had moderate or greater hepatic siderosis, 80% (77/96) had pancreatic siderosis, 4% (3/80) had cardiac siderosis, and 45% (13/29) had pituitary siderosis and/or volume loss. Pancreatic iron was associated with both cardiac (p = .0043) and pituitary iron (p = .0101). In the 73 off-therapy patients, ferritin levels were lower (p = .0008) with higher correlation with liver iron concentration (LIC) (p = .0016) than on-therapy patients. Fifty-eight subjects were treated for IO.

CONCLUSION

In this heavily treated cohort of pediatric cancer patients, more than 80% had extrahepatic iron loading, which occurs with significant exposure to toxic forms of iron related to decreased marrow activity in setting of transfusions. Further studies should examine the effects of exposure to reactive iron on long-term outcomes and potential strategies for management.

Applications of Boron Cluster Supramolecular Frameworks as Metal-Free Chemodynamic Therapy Agents for Melanoma

Chemodynamic therapy (CDT) is a highly targeted approach to treat cancer since it converts hydrogen peroxide into harmful hydroxyl radicals (OH·) through Fenton or Fenton-like reactions. However, the systemic toxicity of metal-based CDT agents has limited their clinical applications. Herein, a metal-free CDT agent: 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT)/ [closo-B12 H12 ]2- (TPT@ B12 H12 ) is reported. Compared to the traditional metal-based CDT agents, TPT@B12 H12 is free of metal avoiding cumulative toxicity during long-term therapy. Density functional theory (DFT) calculation revealed that TPT@B12 H12 decreased the activation barrier more than 3.5 times being a more effective catalyst than the Fe2+ ion (the Fenton reaction), which decreases the barrier about twice. Mechanismly, the theory calculation indicated that both [B12 H12 ]-· and [TPT-H]2+ have the capacity to decompose hydrogen into 1 O2 , OH·, and O2 -· . With electron paramagnetic resonance and fluorescent probes, it is confirmed that TPT@B12 H12 increases the levels of 1 O2 , OH·, and O2 -· . More importantly, TPT@B12 H12 effectively suppress the melanoma growth both in vitro and in vivo through 1 O2 , OH·, and O2 -· generation. This study specifically highlights the great clinical translational potential of TPT@B12 H12 as a CDT reagent.

Iron as an emerging therapeutic target in critically ill patients

The multiple roles of iron in the body have been known for decades, particularly its involvement in iron overload diseases such as hemochromatosis. More recently, compelling evidence has emerged regarding the critical role of non-transferrin bound iron (NTBI), also known as catalytic iron, in the care of critically ill patients in intensive care units (ICUs). These trace amounts of iron constitute a small percentage of the serum iron, yet they are heavily implicated in the exacerbation of diseases, primarily by catalyzing the formation of reactive oxygen species, which promote oxidative stress. Additionally, catalytic iron activates macrophages and facilitates the growth of pathogens. This review aims to shed light on this underappreciated phenomenon and explore the various common sources of NTBI in ICU patients, which lead to transient iron dysregulation during acute phases of disease. Iron serves as the linchpin of a vicious cycle in many ICU pathologies that are often multifactorial. The clinical evidence showing its detrimental impact on patient outcomes will be outlined in the major ICU pathologies. Finally, different therapeutic strategies will be reviewed, including the targeting of proteins involved in iron metabolism, conventional chelation therapy, and the combination of renal replacement therapy with chelation therapy.

Iron Load Toxicity in Medicine: From Molecular and Cellular Aspects to Clinical Implications

Iron is essential for all organisms and cells. Diseases of iron imbalance affect billions of patients, including those with iron overload and other forms of iron toxicity. Excess iron load is an adverse prognostic factor for all diseases and can cause serious organ damage and fatalities following chronic red blood cell transfusions in patients of many conditions, including hemoglobinopathies, myelodyspasia, and hematopoietic stem cell transplantation. Similar toxicity of excess body iron load but at a slower rate of disease progression is found in idiopathic haemochromatosis patients. Excess iron deposition in different regions of the brain with suspected toxicity has been identified by MRI T2* and similar methods in many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Based on its role as the major biological catalyst of free radical reactions and the Fenton reaction, iron has also been implicated in all diseases associated with free radical pathology and tissue damage. Furthermore, the recent discovery of ferroptosis, which is a cell death program based on free radical generation by iron and cell membrane lipid oxidation, sparked thousands of investigations and the association of iron with cardiac, kidney, liver, and many other diseases, including cancer and infections. The toxicity implications of iron in a labile, non-protein bound form and its complexes with dietary molecules such as vitamin C and drugs such as doxorubicin and other xenobiotic molecules in relation to carcinogenesis and other forms of toxicity are also discussed. In each case and form of iron toxicity, the mechanistic insights, diagnostic criteria, and molecular interactions are essential for the design of new and effective therapeutic interventions and of future targeted therapeutic strategies. In particular, this approach has been successful for the treatment of most iron loading conditions and especially for the transition of thalassemia from a fatal to a chronic disease due to new therapeutic protocols resulting in the complete elimination of iron overload and of iron toxicity.

Iron Chelation with Deferasirox Suppresses the Appearance of Labile Plasma Iron During Conditioning Chemotherapy Prior to Allogeneic Stem Cell Transplantation

During conditioning chemotherapy prior to allogeneic haematopoietic stem cell transplantation (HSCT), non-transferrin-bound iron and its chelatable form, labile plasma iron (LPI), regularly appear in the blood of patients at high levels of transferrin saturation (TfS). As these free iron species potentially favor infection and mediate transplantation-associated toxicities, chelation therapy could be an approach to improve outcome after transplantation. However, data addressing iron chelation in the immediate peritransplantation period are sparse. In this study, we investigated the influence of iron chelation with deferasirox during conditioning chemotherapy on the appearance of LPI, the incidence of infection and toxicities, and the tolerability of this treatment in the peritransplantation period. We conducted this single-center prospective observational study in 25 adults with iron overload (serum ferritin >1000 µg/L) undergoing allogeneic HSCT after myeloablative busulfan-based conditioning chemotherapy. Patients received iron chelation with deferasirox (14 mg/kg) from the start of conditioning until day 3 post-transplantation. Iron parameters, including LPI, were obtained at the chelator's trough level daily until day 0 and then on days 4, 7, and 14. Data on infection (bacteremia or invasive fungal disease) and toxicity, as well as the tolerability of deferasirox, were collected until the end of the follow-up period on day 28. Data were analyzed descriptively. TfS levels exceeded 70% in median on 6 days (range, 4 to 10 days) and in 63.6% (range, 36.4% to 90.9%) of the samples per patient, although in 19 of 25 patients (76%), no elevated LPI values were detected during the intake of deferasirox despite high TfS levels. Only 6 patients (24%) showed mildly increased LPI values (≤0.5 units) during the intake of deferasirox, 3 of whom had presented with elevated LPI values before the start of conditioning. Deferasirox was well tolerated, and no aggravation of toxicities was observed. Infection occurred in 5 patients (20%), including 3 of the 6 patients with elevated LPI values despite chelation therapy. In the present study, we demonstrate that iron chelation with deferasirox safely suppresses the appearance of LPI and might decrease the incidence of infection, whereas the impact on transplantation-associated toxicities remains to be elucidated.

Unbalance in Iron Metabolism in Childhood Leukemia Converges with Treatment Intensity: Biochemical and Clinical Analysis

Simple Summary

In children undergoing therapy for acute leukemia or after hematopoietic cell transplantation, the following iron metabolism parameters were analyzed in the context of iron overload: (1) parameters measuring functional and storage iron pools: non-transferrin-bound iron (NTBI) and labile plasma iron (LPI) levels, iron, transferrin, total iron-binding capacity, ferritin, ferritin heavy and light chains; (2) proteins regulating iron absorption and its release from tissue stores: hepcidin, soluble hemojuvelin, soluble ferroportin-1; (3) proteins regulating the erythropoietic activity of bone marrow: erythroferrone, erythropoietin, soluble transferrin receptor. It has been shown that the occurrence of NTBI and LPI in the circulation and the intensification of disturbances in iron metabolism were associated with the intensity of anti-leukemic treatment and were the highest in the transplant group followed by the acute leukemia after treatment and de novo groups. In patients after transplantation, the most significant changes were found in NTBI, LPI, iron, ferritin, hepcidin, and ferroportin-1 levels.

Abstract

Objective: The aim of this study was to evaluate non-transferrin-bound iron (NTBI) and labile plasma iron (LPI) levels and other parameters of iron metabolism in children undergoing therapy for acute leukemia or after hematopoietic cell transplantation (HCT), in the context of iron overload. Patients: A total number of 85 children were prospectively included into four groups: controls, acute leukemia de novo, acute leukemia after intensive treatment, and after HCT. Methods: The following iron metabolism parameters were analyzed: (1) parameters measuring functional and storage iron pools: NTBI, LPI, iron, transferrin, total iron-binding capacity, ferritin, ferritin heavy and light chains; (2) proteins regulating iron absorption and its release from tissue stores: hepcidin, soluble hemojuvelin, soluble ferroportin-1; (3) proteins regulating the erythropoietic activity of bone marrow: erythroferrone, erythropoietin, soluble transferrin receptor. Results: Intensive treatment of leukemia in children was associated with the presence of serum NTBI and LPI, which was the highest in the HCT group followed by the acute leukemia after treatment and de novo groups. In patients after HCT, the most significant changes were found in NTBI, LPI, iron, ferritin, hepcidin, and ferroportin-1 levels. Conclusions: The occurrence of NTBI and LPI in the circulation and the intensification of disturbances in iron metabolism were associated with the intensity of the anti-leukemic treatment.

Iron overload in the HCT patient: a review

Iron overload (IO) is common in hematologic malignancies and hemoglobinopathies, largely due to red cell transfusion burden. End-organ damage from IO occurs via reactive oxygen species-mediated pathways. The impact of pretransplant IO on hematopoietic cell transplant (HCT) morbidity and mortality remains contentious; studies have shown mixed results, possibly due to variability in study population and design, as well as markers of IO. Ferritin has served as a traditional circulating marker of total body IO, but liver iron content by MRI appears to be a better marker of end-organ involvement. Novel surrogate markers including hepcidin, marrow Prussian blue staining, and labile plasma iron levels may prove to be more specific for HCT complications. Posttransplant phlebotomy, chelation, or both in combination remains the mainstays of treatment, though may ultimately be supplanted by pretransplant or peri-transplant use of bone marrow maturation agents or targeted chelation at time of highest IO risk. This review discusses the pathophysiology of IO in hematologic disease, the evidence supporting and refuting its negative impact on HCT outcomes, as well as current and future therapies.

Iron overload in transfusion-dependent patients

Before the advent of effective iron chelation, death from iron-induced cardiomyopathy occurred in the second decade in patients with transfusion-dependent chronic anemias. The advances in our understanding of iron metabolism; the ability to monitor iron loading in the liver, heart, pancreas and pituitary; and the availability of several effective iron chelators have dramatically improved survival and reduced morbidity from transfusion-related iron overload. Nevertheless, significantly increased survival brings about new complications such as malignant transformation resulting from prolonged exposure to iron, which need to be considered when developing long-term therapeutic strategies. This review discusses the current biology of iron homeostasis and its close relation to marrow activity in patients with transfusion-dependent anemias, and how biology informs clinical approach to treatment.

Transferrin and transferrin receptors update

In vertebrates, transferrin (Tf) safely delivers iron through circulation to cells. Tf-bound iron is incorporated through Tf receptor (TfR) 1-mediated endocytosis. TfR1 can mediate cellular uptake of both Tf and H-ferritin, an iron storage protein. New World arenaviruses, which cause hemorrhagic fever, and Plasmodium vivax use TfR1 for entry into host cells. Human TfR2, another receptor for Tf, is predominantly expressed in hepatocytes and erythroid precursors, and holo-Tf dramatically upregulates its expression. TfR2 forms a complex with hemochromatosis protein, HFE, and serves as a component of the iron sensing machinery in hepatocytes. Defects in TfR2 cause systemic iron overload, hemochromatosis, through down-regulation of hepcidin. In erythroid cells, TfR2 forms a complex with the erythropoietin receptor and regulates erythropoiesis. TfR2 facilitates iron transport from lysosomes to mitochondria in erythroblasts and dopaminergic neurons. Administration of apo-Tf, which scavenges free iron, has been explored for various clinical conditions including atransferrinemia, iron overload, and tissue ischemia. Apo-Tf has also been shown to ameliorate anemia in animal models of β-thalassemia. In this review, I provide an update and summary on our knowledge of mammalian Tf and its receptors.

Improved survival outcomes and restoration of graft-vs-leukemia effect by deferasirox after allogeneic stem cell transplantation in acute myeloid leukemia

Deferasirox is an oral iron-chelating agent having possible antileukemia and immune modulatory effects. Few reports have evaluated deferasirox in the setting of allogeneic hematopoietic stem cell transplantation (allo-HSCT). We investigated the impact of deferasirox after allo-HSCT in acute myeloid leukemia (AML). Of 326 consecutive patients undergoing allo-HSCT in remission, analysis of 198 patients not receiving deferasirox revealed the negative prognostic effect of hyperferritinemia (≥1000 ng/mL) before and after allo-HSCT on survival mainly due to increase in relapse. Of 276 patients with hyperferritinemia at 1 month after allo-HSCT, 128 patients (46%) received deferasirox. Deferasirox induced a faster decline in serum ferritin level with a manageable safety profile, which significantly reduced relapse rather than nonrelapse mortality, resulting in better survival compared to patients not receiving deferasirox. Of note, the deferasirox group had a significantly higher incidence of chronic graft-vs-host disease, indicating improved graft-vs-leukemia (GVL) effects evidenced by the presence of suppressed regulatory T cells and sustained higher proportion of NK cells in peripheral blood. This study firstly demonstrates the improved survival and restoration of GVL effects of patients with AML by deferasirox, which also clarifies the detrimental effect of hyperferritinemia through after allo-HSCT.

Iron overload in myelodysplastic syndromes: Evidence based guidelines from the Canadian consortium on MDS

In 2008 the first evidence-based Canadian consensus guideline addressing the diagnosis, monitoring and management of transfusional iron overload in patients with myelodysplastic syndromes (MDS) was published. The Canadian Consortium on MDS, comprised of hematologists from across Canada with a clinical and academic interest in MDS, reconvened to update these guidelines. A literature search was updated in 2017; topics reviewed include mechanisms of iron overload induced cellular damage, evidence for clinical endpoints impacted by iron overload including organ dysfunction, infections, marrow failure, overall survival, acute myeloid leukemia progression, and endpoints around hematopoietic stem-cell transplant. Evidence for an impact of iron reduction on the same endpoints is discussed, guidelines are updated, and areas identified where evidence is suboptimal. The guidelines address common questions around the diagnosis, workup and management of iron overload in clinical practice, and take the approach of who, when, why and how to treat iron overload in MDS. Practical recommendations for treatment and monitoring are made. Evidence levels and grading of recommendations are provided for all clinical endpoints examined.

Iron overload is correlated with impaired autologous stem cell mobilization and survival in acute myeloid leukemia

BACKGROUND

Patients with acute myeloid leukemia (AML) undergoing consolidation with autologous stem cell transplantation (ASCT) depend on the successful mobilization of peripheral blood stem cells. However, the factors affecting the mobilization potential in AML patients and, in particular, the effect of transfusion-related iron overload on peripheral blood stem cell mobilization are largely unknown.

STUDY DESIGN AND METHODS

We investigated the association of varying levels of iron overload and stem cell mobilization efficacy in consecutive AML patients after two induction cycles.

RESULTS

A total of 113 AML patients in early first complete remission underwent the mobilization procedure. While 84 (74.3%) patients had serum ferritin levels exceeding 1000 μg/L, 26 (23.0%) patients had levels even higher than 2000 μg/L. Iron overload correlated with the number of preceding red blood cell transfusions and inversely correlated with circulating CD34+ cell levels (p = 0.04) at apheresis. Finally, the median progression-free and overall survival rates of patients with ferritin levels of higher than 2000 μg/L were shorter with 332 days versus 2156 days (p = 0.04) and 852 days versus 2235 days (p = 0.04), respectively.

CONCLUSION

Our data suggest that transfusion-related iron overload is suppressing the mobilization potential and is associated with inferior outcome in AML.

The Tumor Suppressor, P53, Decreases the Metal Transporter, ZIP14

Loss of p53’s proper function accounts for over half of identified human cancers. We identified the metal transporter ZIP14 (Zinc-regulated transporter (ZRT) and Iron-regulated transporter (IRT)-like Protein 14) as a p53-regulated protein. ZIP14 protein levels were upregulated by lack of p53 and downregulated by increased p53 expression. This regulation did not fully depend on the changes in ZIP14’s mRNA expression. Co-precipitation studies indicated that p53 interacts with ZIP14 and increases its ubiquitination and degradation. Moreover, knockdown of p53 resulted in higher non-transferrin-bound iron uptake, which was mediated by increased ZIP14 levels. Our study highlights a role for p53 in regulating nutrient metabolism and provides insight into how iron and possibly other metals such as zinc and manganese could be regulated in p53-inactivated tumor cells.

Management of iron overload in hemoglobinopathies: what is the appropriate target iron level?

Patients with thalassemia become iron overloaded from increased absorption of iron, ineffective erythropoiesis, and chronic transfusion. Before effective iron chelation became available, thalassemia major patients died of iron-related cardiac failure in the second decade of life. Initial treatment goals for chelation therapy were aimed at levels of ferritin and liver iron concentrations associated with prevention of adverse cardiac outcomes and avoidance of chelator toxicity. Cardiac deaths were greatly reduced and survival was much longer. Epidemiological data from the general population draw clear associations between increased transferrin saturation (and, by inference, labile iron) and early death, diabetes, and malignant transformation. The rate of cancers now seems to be significantly higher in thalassemia than in the general population. Reduction in iron can reverse many of these complications and reduce the risk of malignancy. As toxicity can result from prolonged exposure to even low levels of excess iron, and survival in thalassemia patients is now many decades, it would seem prudent to refocus attention on prevention of long-term complications of iron overload and to maintain labile iron and total body iron levels within a normal range, if expertise and resources are available to avoid complications of overtreatment.

Toxicity of iron overload and iron overload reduction in the setting of hematopoietic stem cell transplantation for hematologic malignancies

Iron is an essential element for key cellular metabolic processes. However, transfusional iron overload (IOL) may result in significant cellular toxicity. IOL occurs in transfusion dependent hematologic malignancies (HM), may lead to pathological clinical outcomes, and IOL reduction may improve outcomes. In hematopoietic stem cell transplantation (SCT) for HM, IOL may have clinical importance; endpoints examined regarding an impact of IOL and IOL reduction include transplant-related mortality, organ function, infection, relapse risk, and survival. Here we review the clinical consequences of IOL and effects of IOL reduction before, during and following SCT for HM. IOL pathophysiology is discussed as well as available tests for IOL quantification including transfusion history, serum ferritin level, transferrin saturation, hepcidin, labile plasma iron and other parameters of iron-catalyzed oxygen free radicals, and organ IOL by imaging. Data-based recommendations for IOL measurement, monitoring and reduction before, during and following SCT for HM are made.

Organ iron accumulation in chronically transfused children with sickle cell anaemia: baseline results from the TWiTCH trial

Transcranial Doppler (TCD) With Transfusions Changing to Hydroxyurea (TWiTCH) trial is a randomized, open-label comparison of hydroxycarbamide (also termed hydroxyurea) versus continued chronic transfusion therapy for primary stroke prevention in patients with sickle cell anaemia (SCA) and abnormal TCD. Severity and location of iron overload is an important secondary outcome measure. We report the baseline findings of abdominal organ iron burden in 121 participants. At enrollment, patients were young (9·8 ± 2·9 years), predominantly female (60:40), and previously treated with transfusions (4·1 ± 2·4 years) and iron chelation (3·1 ± 2·1 years). Liver iron concentration (LIC; 9·0 ± 6·6 mg/g dry weight) and serum ferritin were moderately elevated (2696 ± 1678 μg/l), but transferrin was incompletely saturated (47·2 ± 23·6%). Spleen R2* was 509 ± 399 Hz (splenic iron ~13·9 mg/g) and correlated with LIC (r(2)  = 0·14, P = 0·0008). Pancreas R2* was increased in 38·3% of patients but not to levels associated with endocrine toxicity. Kidney R2* was increased in 80·7% of patients; renal iron correlated with markers of intravascular haemolysis and was elevated in patients with increased urine albumin-creatinine ratios. Extra-hepatic iron deposition is common among children with SCA who receive chronic transfusions, and could potentiate oxidative stress caused by reperfusion injury and decellularized haemoglobin.

Iron toxicity and its possible association with treatment of Cancer: lessons from hemoglobinopathies and rare, transfusion-dependent anemias

Exposure to elevated levels of iron causes tissue damage and organ failure, and increases the risk of cancer. The toxicity of iron is mediated through generation of oxidants. There is also solid evidence indicating that oxidant stress plays a significant role in a variety of human disease states, including malignant transformation. Iron toxicity is the main focus when managing thalassemia. However, the short- and long-term toxicities of iron have not been extensively considered in children and adults treated for malignancy, and only recently have begun to draw oncologists' attention. The treatment of malignancy can markedly increase exposure of patients to elevated toxic iron species without the need for excess iron input from transfusion. This under-recognized exposure likely enhances organ toxicity and may contribute to long-term development of secondary malignancy and organ failure. This review discusses the current understanding of iron metabolism, the mechanisms of production of toxic free iron species in humans, and the relation of the clinical marker, transferrin saturation (TS), to the presence of toxic free iron. We will present epidemiological data showing that high TS is associated with poor outcomes and development of cancer, and that lowering free iron may improve outcomes. Finally, we will discuss the possible relation between some late complications seen in survivors of cancer and those due to iron toxicity.

Non transferrin bound iron (NTBI) in acute leukemias throughout conventional intensive chemotherapy: kinetics of its appearance and potential predictive role in infectious complications

We analyzed appearance of non transferrin bound iron (NTBI) in 30 transplant eligible patients with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) during conventional chemotherapy treatment program and evaluated possible relationship with transfusional body iron intake, iron parameters and clinical complications. For each course, serum samples for NTBI detection were taken prior to chemotherapy, during treatment and during subsequent bone marrow myelosuppression: NTBI was assessed by HPLC. Appearance of NTBI was observed from the start of induction treatment and was still detectable during bone marrow myelosuppression; the recovery of the bone marrow function coincided with the disappearance of NTBI. This kinetic was observed in all subsequent high doses chemotherapy courses, independently from confounding variables such as transfusional iron intake and transferrin saturation. NTBI seems to be a consequence of chemotherapy induced lysis of bone marrow cells and, partly, of hepatocytes after cytotoxic injury. The subsequent persistence of NTBI throughout bone marrow myelosuppression is related to the transient suspension of erythropoietic activity. Moreover, NTBI levels >2μM at the beginning of iatrogenic myelosuppression were associated with higher risk of sepsis caused by Gram negative Bacilli (RR 2.571), also compared with other infectious complications (RR 1.954).

Assessment of labile plasma iron in patients who undergo hematopoietic stem cell transplantation

Body iron disorders have been reported after myeloablative conditioning in patients undergoing hematopoietic stem cell transplantation (HSCT). There is a concern that labile plasma iron (LPI), the redox-active form of iron, can be involved in the occurrence of toxicity and other complications commonly observed in the early post-HSCT period. In order to better understand the LPI kinetics and its determinants and implications, we undertook sequential LPI determinations before and after conditioning until engraftment in 25 auto-HSCT patients. Increased LPI was present in only 5 patients before starting conditioning. Shortly after conditioning, LPI levels were increased in 23 patients, with peak at day 0, returning to normal range upon engraftment in 21 patients. Overall, LPI levels correlated weakly with serum ferritin and more strongly with transferrin saturation; however, both parameters were apparently not applicable as surrogate markers for increased LPI. Although this was a small cohort, logistic regression suggested that baseline LPI levels could predict occurrence of grade III or IV toxicity. In conclusion, LPI kinetics is influenced by aplasia following conditioning and engraftment. Measuring LPI before starting conditioning can offer an opportunity to predict toxicity and, perhaps, the need for chelation therapy.

Tissue iron evaluation in chronically transfused children shows significant levels of iron loading at a very young age

Chronic blood transfusions start at a very young age in subjects with transfusion-dependent anemias, the majority of whom have hereditary anemias. To understand how rapidly iron overload develops, we retrospectively reviewed 308 MRIs for evaluation of liver, pancreatic, or cardiac iron in 125 subjects less than 10 years old. Median age at first MRI evaluation was 6.0 years. Median liver iron concentrations in patients less than 3.5 years old were 14 and 13 mg/g dry weight in thalassemia major (TM) and Diamond-Blackfan anemia (DBA) patients, respectively. At time of first MRI, pancreatic iron was markedly elevated (> 100 Hz) in DBA patients, and cardiac iron ( R₂* >50 Hz) was present in 5/112 subjects (4.5%), including a 2.5 years old subject with DBA. Five of 14 patients (38%) with congenital dyserythropoietic anemia (CDA) developed excess cardiac iron before their 10th birthday. Thus, clinically significant hepatic and cardiac iron accumulation occurs at an early age in patients on chronic transfusions, particularly in those with ineffective or absent erythropoiesis, such as DBA, CDA, and TM, who are at higher risk for iron cardiomyopathy. Performing MRI for iron evaluation in the liver, heart, and pancreas as early as feasible, particularly in those conditions in which there is suppressed bone marrow activity is very important in the management of iron loaded children in order to prescribe appropriate chelation to prevent long-term sequelae. .

Treating thalassemia major-related iron overload: the role of deferiprone

Over the last 20 years, management for thalassemia major has improved to the point where we predict that patients’ life expectancy will approach that of the normal population. These outcomes result from safer blood transfusions, the availability of three iron chelators, new imaging techniques that allow specific organ assessment of the degree of iron overload, and improvement in the treatment of hepatitis. In October 2011, the Food and Drug Administration licensed deferiprone, further increasing the available choices for iron chelation in the US. The ability to prescribe any of the three chelators as well as their combinations has led to more effective reduction of total body iron. The ability to determine the amount of iron in the liver and heart by magnetic resonance imaging allows the prescription of the most appropriate chelation regime for patients and to reconsider what our aims with respect to total body iron should be. Recent evidence from Europe has shown that by normalizing iron stores not only are new morbidities prevented but also reversal of many complications such as cardiac failure, hypothyroidism, hypogonadism, impaired glucose tolerance, and type 2 diabetes can occur, improving survival and patients’ quality of life. The most effective way to achieve normal iron stores seems to be with the combination of deferoxamine and deferiprone. Furthermore, outcomes should continue to improve in the future. Starting relative intensive chelation in younger children may prevent short stature and abnormal pubertal maturation as well as other iron-related morbidities. Also, further information should become available on the use of other combinations in chelation treatment, some of which have been used only in a very limited fashion to date. All these advances in management require absolute cooperation and understanding of parents, children, and, subsequently, the patients themselves. Only with such cooperation can normal long-term survival be achieved, as adherence to treatment is now likely the primary barrier to longevity.

Does iron overload really matter in stem cell transplantation?

A growing body of evidence suggests that iron overload is associated with inferior outcomes after myeloablative allogeneic hematopoietic stem cell transplantation (HSCT). However, all of those studies used surrogate markers of iron overload, especially serum ferritin, and most had a retrospective design. We conducted a prospective observational study in patients with myelodysplastic syndrome or acute leukemia undergoing myeloablative HSCT. Forty-five patients who were followed for over 1 year, with serial measurements of serum iron parameters, as well as liver and cardiac magnetic resonance imaging. There was no significant increase in ferritin, liver or cardiac iron content in the 12 months following HSCT. Although serum ferritin still appeared to have prognostic significance, as previously reported, pre-HSCT iron overload (as reflected in liver iron content) was not associated with increased mortality, relapse, or graft-versus-host disease. These results raise the possibility that the adverse prognostic impact of pre-HSCT hyperferritinemia may be related to factors independent of iron overload.

Non-transferrin bound iron: a key role in iron overload and iron toxicity

BACKGROUND

Besides transferrin iron, which represents the normal form of circulating iron, non-transferrin bound iron (NTBI) has been identified in the plasma of patients with various pathological conditions in which transferrin saturation is significantly elevated.

SCOPE OF THE REVIEW

To show that: i) NTBI is present not only during chronic iron overload disorders (hemochromatosis, transfusional iron overload) but also in miscellaneous diseases which are not primarily iron overloaded conditions; ii) this iron species represents a potentially toxic iron form due to its high propensity to induce reactive oxygen species and is responsible for cellular damage not only at the plasma membrane level but also towards different intracellular organelles; iii) the NTBI concept may be expanded to include intracytosolic iron forms which are not linked to ferritin, the major storage protein which exerts, at the cellular level, the same type of protective effect towards the intracellular environment as transferrin in the plasma.

MAJOR CONCLUSIONS

Plasma NTBI and especially labile plasma iron determinations represent a new important biological tool since elimination of this toxic iron species is a major therapeutic goal.

GENERAL SIGNIFICANCE

The NTBI approach represents an important mechanistic concept for explaining cellular iron excess and toxicity and provides new important biochemical diagnostic tools. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Iron overload and allogeneic hematopoietic stem-cell transplantation

Iron overload is frequently observed in patients with hematologic diseases before and after allogeneic stem-cell transplantation because they usually receive multiple red blood cell transfusions. Elevated pretransplant serum ferritin levels, which are widely used as indicators of body iron status, are significantly associated with a lower overall survival rate and a higher incidence of treatment-related complications; for example, infections and hepatic veno-occlusive disease. As serum ferritin levels are affected, not only by iron loading but also by inflammation, imaging techniques to quantify tissue iron levels have been developed, for example, quantitative MRI using the transverse magnetic relaxation rate, and superconducting quantum interference devices. Iron chelators, such as deferasirox, a new oral iron-chelating agent, reduce iron load in transfusion-dependent patients. Iron-chelating therapy before and/or after transplantation is a promising strategy to improve the clinical outcomes of transplant patients with iron overload. However, further research is needed to prove the direct relationship between iron overload and adverse outcomes, as well as to determine the effects of treatment for iron overload on outcomes of allogeneic stem-cell transplantation.

Optimizing therapy for iron overload in the myelodysplastic syndromes: recent developments

The myelodysplastic syndromes (MDS) are characterized by cytopenias and risk of progression to acute myeloid leukaemia (AML). Most MDS patients eventually require transfusion of red blood cells for anaemia, placing them at risk of transfusional iron overload. In β-thalassaemia major, transfusional iron overload leads to organ dysfunction and death; however, with iron chelation therapy, organ function is improved, and survival improved to near normal and correlated with the degree of compliance with chelation. In lower-risk MDS, several nonrandomized studies suggest an adverse effect of iron overload on survival and that lowering iron with chelation may minimize this impact. Emerging data indicate that chelation may improve organ function, particularly hepatic function, and a minority of patients may have improvement in cell counts and decreased transfusion requirements. While guidelines for MDS generally recommend chelation in selected lower-risk patients, data from nonrandomized trials suggest iron overload may impact adversely on the outcome of higher-risk MDS and stem cell transplantation (SCT). This effect may be due to increased transplant-related mortality, infection and AML progression, and preliminary data suggest that lowering iron may be beneficial in this patient group. Other areas of active and future investigation include optimizing the monitoring of iron overload using imaging such as T2* MRI and measures of labile iron and oxidative stress; correlating new methods of measuring iron to clinical outcomes; clarifying the contribution of different cellular and extracellular iron pools to iron toxicity; optimizing chelation by using agents that access the appropriate iron pools to minimize the relevant clinical consequences in individual patients; and incorporating measures of quality of life and co-morbidities into clinical trials of chelation in MDS. It should be noted that chelation is costly and potentially toxic, and in MDS should be initiated after weighing potential risks and benefits for each patient until more definitive data are available. In this review, data on the impact of iron overload in MDS and SCT are discussed; for example, several noncontrolled studies show inferior survival in patients with iron overload in these clinical settings, including an increase in transplant-related mortality and infection risk. Possible mechanisms of iron toxicity include oxidative stress, which can damage cellular components, and the documented impact of lowering iron on organ function with measures such as iron chelation therapy includes an improvement in elevated liver transaminases. Lowering iron also appears to improve survival in both lower-risk MDS and SCT in nonrandomized studies. Selected aspects of iron metabolism, transport, storage and distribution that may be amenable to future intervention and improved removal of iron from important cellular sites are discussed, as are attempts to quantify quality of life and the importance of co-morbidities in measures to treat MDS, including chelation therapy.

Iron overload in patients with acute leukemia or MDS undergoing myeloablative stem cell transplantation

Patients with hematologic malignancies undergoing allogeneic stem cell transplantation (HSCT) commonly have an elevated serum ferritin prior to HSCT, which has been associated with increased mortality after transplantation. This has led to the suggestion that iron overload is common and deleterious in this patient population. However, the relationship between serum ferritin and parenchymal iron overload in such patients is unknown. We report a prospective study of 48 patients with acute leukemia (AL) or myelodysplastic syndromes (MDS) undergoing myeloablative HSCT, using magnetic resonance imaging (MRI) to estimate liver iron content (LIC) and cardiac iron. The median (and range) pre-HSCT value of serum ferritin was 1549 ng/mL (20-6989); serum hepcidin, 59 ng/mL (10-468); labile plasma iron, 0 LPI units (0.0-0.9). Eighty-five percent of patients had hepatic iron overload (HIO), and 42% had significant HIO (LIC ≥5.0 mg/gdw). Only 1 patient had cardiac iron overload. There was a strong correlation between pre-HSCT serum ferritin and estimated LIC (r = .75), which was mostly dependent on prior transfusion history. Serum hepcidin was appropriately elevated in patients with HIO. Labile plasma iron elevation was rare. A regression calibration analysis supported the hypothesis that elevated pre-HSCT LIC is significantly associated with inferior post-HSCT survival. These results contribute to our understanding of the prevalence, mechanism, and consequences of iron overload in HSCT.

Pretransplant serum ferritin and C-reactive protein as predictive factors for early bacterial infection after allogeneic hematopoietic cell transplantation

Although fluoroquinolones or other antibiotics are commonly used to prevent bacterial infections after hematopoietic cell transplantation (HCT), because of the growing presence of multidrug-resistant microorganisms, it is important to identify patients who are more likely to benefit from antibacterial prophylaxis. To evaluate risk factors for early bacterial infection after allogeneic HCT, we retrospectively analyzed clinical data for 112 consecutive adult patients with hematological malignancies who received transplants without any antibacterial prophylaxis. The cumulative incidence of bacterial infection at 30 days after transplantation was 16%. Among various pre-transplant factors, only high serum ferritin (>700 ng/mL, 47 patients) and high C-reactive protein (CRP) (>0.3 mg/dL, 28 patients) levels were significantly associated with the development of bacterial infection in a multivariate analysis (hazard ratio (95% confidence interval): ferritin, 4.00 (1.32-12.17); CRP, 3.64 (1.44-9.20)). In addition, septic shock and sepsis with organ failure were exclusively observed in patients who had high ferritin and/or high CRP levels. These results suggest that pretransplant serum ferritin and CRP levels can be useful markers for predicting the risk of early bacterial infection after allogeneic HCT. It may be prudent to limit antibacterial prophylaxis to patients with predefined risk factors to ensure the safety of HCT with the use of fewer antibiotics.

Hepcidin messenger RNA expression in human lymphocytes

Hepcidin regulates intracellular iron levels by interacting with and promoting the degradation of ferroportin, a membrane protein and the only known cellular iron exporter. Studies of hepcidin expression and regulation have focused on its effects in innate immunity and as a regulator of systemic iron metabolism. In the present study we characterized the expression of hepcidin messenger RNA (mRNA) in human peripheral blood mononuclear cells (PBMCs) with a focus on peripheral blood lymphocytes (PBLs). We found that (1) all human PBMCs analyzed express basal hepcidin mRNA levels; (2) hepcidin mRNA expression increases after T-lymphocyte activation; (3) expression by PBLs increases in response to challenge by holotransferrin (Fe-TF) and by ferric citrate in vitro; (4) the Fe-TF-mediated up-regulation of hepcidin decreases ferroportin expression at the cytoplasmic membrane of PBLs; and (5) silencing of tumour necrosis factor-alpha (TNF-alpha) abrogates the effect of Fe-TF. In summary, we show that hepcidin expression determines intracellular iron levels by regulating the expression of ferroportin, as described in other cells, and that inappropriately low expression of hepcidin impairs normal lymphocyte proliferation. The results establish hepcidin as a new player in lymphocyte biology.

Impact of pre-transplant serum ferritin on outcomes of patients with myelodysplastic syndromes or secondary acute myeloid leukaemia receiving reduced intensity conditioning allogeneic haematopoietic stem cell transplantation

We report on a retrospective analysis examining the influence of pre-transplant serum ferritin on transplant outcomes of 99 MDS patients receiving reduced intensity conditioning (RIC) HSCT. The median pre-transplant ferritin value was 1992 ng/ml (range: 6-9580 ng/ml). No patients received iron chelation therapy preceding transplantation. On univariate analysis, there was a strong correlation between a higher pre-transplant serum ferritin (>1500 ng/ml) and a significantly inferior 3-year OS (64.6+/-7.5% vs 39.6+/-7.3%, p=0.01). However, pre-transplant serum ferritin did not influence 3-year TRM (20.2+/-7% vs 27.4+/-7%, p=0.24). There was no difference in infection-related mortality, and incidence of acute or chronic GvHD between cohorts. On multivariate analysis, a raised serum ferritin (HR: 2.00, 95% CI: 0.97-3.57, p=0.03), and the presence of >5% bone marrow blasts at time of transplantation (HR: 2.14, 95% CI: 0.84-4.58, p=0.06) were independent predictors of an inferior overall survival. However, pre-transplant serum ferritin was not a significant predictor of disease-free survival, relapse or TRM. When compared with myeloablative regimens, RIC regimens may attenuate the impact of iron overload related end-organ toxicity. Prospective studies incorporating alternative biomarkers of iron metabolism alongside serum ferritin levels are needed to improve our understanding of the significance of iron overload in MDS patients undergoing allogeneic transplantation.