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Many disorders of iron homeostasis (e.g., iron overload) are associated with the dynamic kinetic profiles of multiple non-transferrin bound iron (NTBI) species, chronic exposure to which is associated with deleterious end-organ effects. Here we discuss the chemical nature of NTBI species, challenges with measuring NTBI in plasma, and the clinical relevance of NTBI exposure based on source (iron overload disorder vs. intravenous iron-carbohydrate complex administration). NTBI is not a single entity but consists of multiple, often poorly characterized species, some of which are kinetically non-exchangeable while others are relatively exchangeable. Prolonged presence of plasma NTBI is associated with excessive tissue iron accumulation in susceptible tissues, with consequences, such as endocrinopathy and heart failure. In contrast, intravenous iron-carbohydrate nanomedicines administration leads only to transient NTBI appearance and lacks evidence for association with adverse clinical outcomes. Assays to measure plasma NTBI are typically technically complex and remain chiefly a research tool. There have been two general approaches to estimating NTBI: capture assays and redox-activity assays. Early assays could not avoid capturing some iron from transferrin, thus overestimating NTBI. By contrast, some later assays may have promoted the donation of NTBI species to transferrin during the assay procedure, potentially underestimating NTBI levels. The levels of transferrin saturation at which NTBI species have been detectable have varied between different methodologies and between patient populations studied.

Vaccines are the most effective measure to prevent deaths and illness from infectious diseases. Nevertheless, the efficacy of several paediatric vaccines is lower in low-income and middle-income countries (LMICs), where mortality from vaccine-preventable infections remains high. Vaccine efficacy can also be decreased in adults in the context of some common comorbidities. Identifying and correcting the specific causes of impaired vaccine efficacy is of substantial value to global health. Iron deficiency is the most common micronutrient deficiency worldwide, affecting more than 2 billion people, and its prevalence in LMICs could increase as food security is threatened by the COVID-19 pandemic. In this Viewpoint, we highlight evidence showing that iron deficiency limits adaptive immunity and responses to vaccines, representing an under-appreciated additional disadvantage to iron deficient populations. We propose a framework for urgent detailed studies of iron-vaccine interactions to investigate and clarify the issue. This framework includes retrospective analysis of newly available datasets derived from trials of COVID-19 and other vaccines, and prospective testing of whether nutritional iron interventions, commonly used worldwide to combat anaemia, improve vaccine performance.

Autoimmune gastritis (AIG) is a chronic, autoimmune disease characterized by atrophy of the oxyntic glands of the stomach. In this Primer, Di Sabatino and colleagues discuss the epidemiology, novel insights in AIG pathogenesis, diagnostic challenges and current therapeutic options. Autoimmune gastritis (AIG) is an increasingly prevalent, organ-specific, immune-mediated disorder characterized by the destruction of gastric parietal cells, leading to the loss of intrinsic factor and reduced acid output. These alterations result in malabsorption of iron, vitamin B-12(pernicious anaemia) and potentially other micronutrients. For several years, most studies have focused on pernicious anaemia only, generating confusion between the two entities. In AIG, the gastric proton pump, H+/K(+)ATPase, is the major autoantigen recognized by autoreactive T cells. The T cell-dependent activation of B cells stimulates the production of anti-parietal cell antibodies, the serological hallmark of AIG. The role ofHelicobacter pyloriinfection in activating or favouring the autoimmune process is still uncertain. Early histopathological alterations allowing a more precise and prompt recognition have recently been described. AIG is burdened by a substantial diagnostic delay as it can present with varied clinical signs including, among others, gastrointestinal symptoms and neuropsychiatric manifestations. In advanced stages, AIG might progress to neuroendocrine tumours and gastric adenocarcinoma. Management includes early detection through a proactive case-finding strategy, micronutrient supplementation and endoscopic surveillance. This Primer comprehensively describes the most important insights regarding the epidemiology, pathophysiology, diagnosis and management of AIG, focusing on the most controversial, outstanding issues and future directions.

In this study we explore the antimalarial effects of 3-hydroxypyridin-4-ones (CP compounds), a family of bidentate orally effective iron chelators in experimental animal systems in vivo and in vitro, and examine whether the iron chelator deferoxamine (DF) is active against human infection with P. falciparum. There was direct relation between lipid solubility of the CP compounds, which would facilitate membrane transit, and their in vivo antimalarial action, suggesting direct intracellular iron chelation as the most likely explantation for the antimalarial effect of iron chelators. Results of the double-blind, placebo controlled trial of DF in humans with asymptomatic parasitemia provided unequivocal evidence that this iron-chelating agent has antimalarial activity. Depriving the parasite of a metabolically important source of iron may represent a novel approach to antimalarial drug development. DF is a relatively ineffective intraerythrocytic chelator, and our data indicate that other orally effective iron chelators may have superior antimalarial activity in vivo. A systematic screening of available iron chelating drugs may result in the identification of potentially useful antimalarial compounds.

Iron overload in myelodysplastic syndrome (MDS) results from multiple RBC-transfusions and inappropriate increased iron absoption associated with ineffective erythropoiesis. Data from hereditary iron-loading anemias indicate long-term consequences of iron toxicity are preventable and potentially reversible by effective iron-chelation therapy (ICT). There is increasing interest in using ICT in persons with MDS because of the recent introduction of orally effective iron-chelators which are suitable for older persons, (1-4). Ideally, evidence supporting the benefit of ICT in MDS should be evidenced-based, especially data from randomized trials showing better survival and, in exceptional cases, improved heart function . Such data are lacking. Nevertheless, it is possible to rely on the extensive data from trials of ICT in persons with thalassemia and to use well-defined predictors of increased risks of life-threatening complications to identify persons with MDS most likely to benefit from iron-chelating therapy.

In thalassemia major, iron overload is the joint outcome of multiple blood transfusions and an inappropriately increased iron absorption associated with ineffective erythropoiesis. Threshold values for iron toxicity are a liver iron concentration exceeding 440 mmoles/g dry weight, serum ferritin >2500 ng/mL, DFO urinary iron excretion >20 mg/day, and transferrin saturation >75%. The outpouring of catabolic iron that exceeds the iron-carrying capacity of transferrin results in the emergence of non-transferrin-bound iron (NTBI). NTBI is cleared preferentially by the liver and myocardium at a rate exceeding 200 times that of transferrin iron. NTBI catalyzes the formation of free radicals, resulting in oxidative stress and damage to mitochondria, lysosomes, lipid membranes, proteins, and DNA. The long-term consequences of iron toxicity, including cirrhosis, myocardiopathy, and endocrine disorders, are preventable and mostly reversible by effective iron chelation therapy. Recent technologic advances in the documentation of organ-specific siderosis and the improved efficiency of iron chelating programs resulted in a spectacular improvement in the prevention of iron-induced end-organ failure and improved survival in thalassemic patients.

A 38-year-old woman developed chronic myeloid leukaemia after 2 years of lithium carbonate therapy. A peculiar feature of her leukaemia, as well as of the 5 patients previously reported in whom CML has developed in the course of lithium therapy, was the unusually high degree of granulocyte maturation manifested in normal leucocyte alkaline phosphatase (LAP) score and, in 1 case, selective increase of transcobalamin III. Although a cause and effect relation between lithium therapy and CML has not yet been established, in view of the stimulatory effect of lithium on granulocyte proliferation, such treatment should be avoided in patients with established myeloproliferative disorders, or in patients at high risk of developing leukaemia.

Despite elegant regulatory mechanisms, iron deficiency anemia (IDA) remains one of the most common nutritional deficiencies of mankind. Iron deficiency is the result of an interplay between increased host requirements, limited external supply, and increased blood loss. When related to increased physiologic needs associated with normal development, iron deficiency is designated physiologic or nutritional. By contrast, pathological iron deficiency, with the exception of gross menorrhagia, is most often the result of gastrointestinal disease associated with abnormal blood loss or malabsorption. If gastroenterologic evaluation fails to disclose a likely cause of IDA, or in patients refractory to oral iron treatment, screening for celiac disease (anti-tissue transglutaminase antibodies), autoimmune gastritis (gastrin, anti-parietal or anti-intrinsic factor antibodies), and Helicobacter pylori (IgG antibodies and urease breath test) is recommended. Recent studies indicate that 20–27% of patients with unexplained IDA have autoimmune gastritis, about 50% have evidence of active H. pylori infection, and 4–6% have celiac disease. The implications for abnormal iron absorption of celiac disease or autoimmune gastritis are obvious. In patients with unexplained IDA and H. pylori infection, cure of refractory IDA by H. pylori eradication offers strong evidence for a cause-and-effect relation between H. pylori infection and unexplained IDA. Stratification by age cohorts in autoimmune gastritis implies a disease presenting as IDA many years before the establishment of clinical cobalamin deficiency. It is likely caused by an autoimmune process triggered by antigenic mimicry between H. pylori epitopes and major autoantigens of the gastric mucosa. Recognition of the respective roles of H. pylori and autoimmune gastritis in the pathogenesis of iron deficiency may have a strong impact on the diagnostic workup and management of unexplained, or refractory IDA.

Before the introduction of erythropoiesis-stimulating agents (ESAs) in 1989, repeated transfusions given to patients with end-stage renal disease caused iron overload, and the need for supplemental iron was rare. However, with the widespread introduction of ESAs, it was recognized that supplemental iron was necessary to optimize hemoglobin response and allow reduction of the ESA dose for economic reasons and recent concerns about ESA safety. Iron supplementation was also found to be more efficacious via intravenous compared to oral administration, and the use of intravenous iron has escalated in recent years. The safety of various iron compounds has been of theoretical concern due to their potential to induce iron overload, oxidative stress, hypersensitivity reactions, and a permissive environment for infectious processes. Therefore, an expert group was convened to assess the benefits and risks of parenteral iron, and to provide strategies for its optimal use while mitigating the risk for acute reactions and other adverse effects. Fil: Macdougall, Iain C.. King's College Hospital Nhs Foundation Trust; Reino Unido Fil: Bircher, Andreas J.. Universitatsspital Basel; Suiza Fil: Eckardt, Kai Uwe. Universitat Erlangen-nuremberg; Alemania Fil: Obrador, Gregorio T.. Universidad Panamericana; México Fil: Pollock, Carol A.. The University Of Sydney; Australia. Royal North Shore Hospital; Australia Fil: Stenvinkel, Peter. Karolinska University Hospital; Suecia Fil: Swinkels, Dorine W.. Radboud University Nijmegen Medical Centre; Países Bajos Fil: Wanner, Christoph. Universitatsklinikum Wurzburg; Alemania Fil: Weiss, Günter. Medizinische Universitat Innsbruck; Austria Fil: Chertow, Glenn M.. University Of Stanford; Estados Unidos Fil: Toblli, Jorge Eduardo. Hospital Alemán. Laboratorio de Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Medicina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The subtle balance between proinflammatory and antiinflammatory cytokines plays an important role in determining the severity of the inflammatory reaction and in the anomalous iron handling associated with infection. Conversely, iron deficiency per se appears to limit the severity of the inflammatory response. All of these considerations are at present highly speculative and in need of further experimental and epidemiologic support. If confirmed, the beneficial biological effects of iron depletion may have a defensive role in inflammation and may be perturbed by the nonselective administration of iron to iron-replete patients who would not benefit from such treatment in the first place. In view of the importance of non-transferrin-bound plasma iron (NTBI) in iron toxicity and its rapid cellular uptake, it may play an important role in the harmful effects of iron in infection, and this is illustrated by the infectious complications of parenteral iron therapy in tropical countries.

Background and Objectives: Since gastric acidity and ascorbate play a critical role in the solubilization and reduction of iron for subsequent absorption, the achlorhydria associated with autoimmune and Helicobacter pylori gastritis may explain the poor response of such patients to oral iron treatment. In order to circumvent this problem, we explored the therapeutic potential of a duodenal formulation of ferrous glycine sulfate consisting of micropellets that do not dissolve at the acid environment of the stomach but, owing to their solubility at a higher pH, discharge their content directly into the duodenum. Design and Methods: In a case-control study, the treatment results of 39 patients with iron deficiency anemia receiving a duodenal formulation of ferrous glycine sulfate (group A) were compared with the results of 39 patients receiving other oral iron compounds (group B). Autoimmune gastritis, H. pylori gastritis or both were present in over 75% of patients in each group. Results: After 1 and 3 months of treatment, mean hemoglobin in group A increased from 9.5 ± 1.2 to 11.2 ± 1.3 and 12.8 ± 1.3 g/dl, respectively. By comparison, in group B, the corresponding values increased from 9.3 ± 1.3 to 10.2 ± 1.5 (p = 0.019) and 11.1 ± 1.7 g/dl (p = 0.022). A favorable response, defined as a more than 2 g/dl increase in basal hemoglobin or hemoglobin exceeding 12 g/dl, was obtained in 33 of 39 patients in group A compared with only 18 of 39 in group B (p = 0.009). Because of treatment failure, 14 patients in group B were subsequently referred for intravenous ferric sucrose therapy versus only 3 in group A (p < 0.0001). Conversely, of 5 patients in group A managed by intravenous iron prior to referral, 4 became independent of parenteral iron after starting the duodenal formulation of ferrous glycine sulfate. Interpretation and Conclusions: In patients with iron deficiency anemia associated with autoimmune and H. pylori gastritis with a high rate of refractoriness to oral iron treatment, satisfactory response to a duodenal formulation of ferrous glycine sulfate can be elicited in the vast majority of cases, obviating the need for expensive, inconvenient and occasionally risky intravenous iron administration.

Background and objectives Helicobacter pylori infection with, or without coexisting autoimmune gastritis has been implicated in several recent studies as an important cause of IDA in patients with unexplained iron deficiency anemia (IDA). However, the role of H. pylori in the causation of IDA is still unsettled as the vast majority of reported patients were premenopausal women in whom menstrual blood loss was likely the dominant factor determining IDA. Design and methods Prospective study of 44 consecutive male IDA patients referred for hematologic evaluation. Following standard endoscopic studies, all patients were screened for non-bleeding GI conditions including celiac disease, autoimmune gastritis and H. pylori gastritis. All subject with H. pylori infection were offered triple therapy for H. pylori eradication. Results Only 15 patients had a likely source of blood loss identified. The 29 males with “unexplained” IDA were distinguished by their younger age (36 ± 20 vs. 57 ± 17 years p

The prevalence and causes of anemia in the elderly were studied in 142 individuals, aged over 60 years, in a small rural community in which a high prevalence of nutritional anemia in pregnancy and childhood was previously shown. The mean Hb level of elderly subjects was slightly but significantly lower than that of the control group of younger individuals. The mild reduction of Hb in the elderly population was paralleled by a slight but significant reduction in serum iron, red cell folates and serum vitamin B12, and by a slight increase in total iron-binding capacity. Therapeutic trial with folic acid failed to improve Hb levels but iron therapy resulted in a significant increase in about one half of the anemic patients. In the rest of the patients, who failed to respond to either folate or iron therapy, anemia was most probably the consequence of underlying chronic disorders. In order to investigate the nature of the diseases associated with anemia, an additional 104 patients aged over 60 years were studied in a general medical ward in Jerusalem. In this group, a primary nutritional anemia could not be implicated in any of the 15 patients with Hb below 11 g/dl, and the most important causes of anemia were chronic renal failure, metastatic carcinoma, gastrointestinal bleeding and infection. These findings indicate that, although diminished serum iron and red cell folate levels may occasionally be found in elderly subjects, nutritional deficiency is seldom responsible for anemia in this age group, and anemia, when present, is usually the manifestation of a chronic underlying disease.

The effect of maturation on ferritin synthesis in erythroid precursor cells was studied in vitro in a population of rabbit bone marrow cells synchronized by actinomycin D. Undifferentiated hemopoietic stem cells were compared with orthochromatic normoblasts and reticulocytes, following incubation in Krebs-Ringer phosphate buffer containing 40% normal rabbit serum. Apoferritin synthesis was measured by following the incorporation of [3H]amino acids into purified ferritin and was correlated with the rate of total protein synthesis and with the rate of radioiron uptake by whole cells and its incorporation into heme. With increasing cellular maturation, a progressive reduction in both apoferritin and total protein synthesis was observed, with undifferentiated cells synthesizing 12 times more protein and ferritin than reticulocytes. The rate of ferritin synthesis was inversely related to the rate of radioiron uptake by whole cells and radioiron incorporation into heme; the lowest rates of radioiron uptake and heme synthesis were found in undifferentiated cells, and the highest rates were in reticulocytes. Radioiron incorporation into ferritin was higher in orthochromatic normoblasts than in undifferentiated cells, but was very low in reticulocytes. This sequence of events indicates that in developing erythroid precursor cells, ferritin synthesis precedes the synthesis of hemoglobin and provides an intracellular storage compartment for the supply of iron for subsequent incorporation into newly formed hemoglobin.

The mechanism of iron chelation was studied in 16 patients with homozygous β-thalassemia. Following the i.v. infusion of desferrioxamine, chelated iron accumulated in the plasma and its maxima

Iron deficiency is a known complication of achlorhydria and may precede the development of pernicious anemia. Among 160 patients with autoimmune gastritis identified by hypergastrinemia and strongly positive antiparietal antibodies, we explored the overlap between 83 subjects presenting with iron deficiency anemia (IDA), 48 with normocytic indices, and 29 with macrocytic anemia. Compared with macrocytic patients, patients with IDA were 21 years younger (41 +/- 15 years versus 62 +/- 15 years) and mostly women. All groups had a high prevalence of thyroid disease (20%) and diabetes (8%) suggestive of the autoimmune polyendocrine syndrome. Stratification by age cohorts from younger than 20 years to older than 60 years showed a regular and progressive increase in mean corpuscular volume (MCV) from 68 +/- 9 to 95 +/- 16 fl, serum ferritin levels from 4 +/- 2 to 37 +/- 41 microg/L, gastrin level from 166 +/- 118 to 382 +/- 299 pM/L (349 +/- 247 to 800 +/- 627 pg/mL), and a decrease in cobalamin level from 392 +/- 179 to 108 +/- 65 pg/mL. The prevalence of Helicobacter pylori infection was 87.5% at age younger than 20 years, 47% at age 20 to 40 years, 37.5% at 41 to 60 years, and 12.5% at age older than 60 years. These findings challenge the common notion that pernicious anemia is a disease of the elderly and imply a disease starting many years before the establishment of clinical cobalamin deficiency, by an autoimmune process likely triggered by H pylori.

Methods are now available to measure the magnitude of iron accumulation in the heart. Their validation currently relies on indirect evidence and not on chemical estimation in cardiac biopsies. All patients with symptomatic heart disease appear to have abnormal T2* values, but many patients without symptomatic heart disease also have evidence of increased myocardial iron. Although there is no proof to date that increased myocardial iron, as evidenced by abnormal magnetic resonance imaging, carries an adverse prognosis, it is likely that such new information will affect the chelating programme of patients. In these cases, there are a number of options available: (i) ongoing treatment with either desferrioxamine (DFO) or deferiprone may be intensified; (ii) the patient may be switched to the alternative chelator or (iii) combined chelation with both DFO and deferiprone may be started, which is more effective than using either chelator alone. For patients with symptomatic heart disease, continuous intravenous DFO with, or without deferiprone, remains the currently recommended treatment, in view of its documented ability to salvage these patients.

OBJECTIVE We observed that many critically ill patients developed leukocytosis following blood transfusions. To validate this observation and to explore a possible mechanism, a prospective study was designed. DESIGN Prospective, non-interventional study. SETTING Surgical/medical intensive care unit in a university-affiliated community hospital. PATIENTS Consecutive patients who required packed red blood cells transfusion. INTERVENTIONS White blood cell count (mean +/- SD) x 10(9)/L before and 2, 4, 6, 12, and 24 hrs following transfusion of non-filtered packed red cells was measured in 96 patients. MEASUREMENTS AND MAIN RESULTS Twenty patients were septic at the time of transfusion, whereas 76 were not. The incidence of post-transfusion leukocytosis in septic vs. nonseptic patients was 15% vs. 76%, respectively (p

Plasma non-transferrin-bound-iron (NTBI) is believed to be responsible for catalyzing the formation of reactive radicals in the circulation of iron overloaded subjects, resulting in accumulation of oxidation products. We assessed the redox active component of NTBI in the plasma of healthy and β-thalassemic patients. The labile plasma iron (LPI) was determined with the fluorogenic dihydrorhodamine 123 by monitoring the generation of reactive radicals prompted by ascorbate but blocked by iron chelators. The assay was LPI specific since it was generated by physiologic concentrations of ascorbate, involved no sample manipulation, and was blocked by iron chelators that bind iron selectively. LPI, essentially absent from sera of healthy individuals, was present in those of β-thalassemia patients at levels (1-16 μM) that correlated significantly with those of NTBI measured as mobilizer-dependent chelatable iron or desferrioxamine chelatable iron. Oral treatment of patients with deferiprone (L1) raised plasma NTBI due to iron mobilization but did not lead to LPI appearance, indicating that L1-chelated iron in plasma was not redox active. Moreover, oral L1 treatment eliminated LPI in patients. The approach enabled the assessment of LPI susceptibility to in vivo or in vitro chelation and the potential of LPI to cause tissue damage, as found in iron overload conditions. (Blood. 2003;102:2670-2677)

Before 1987, iron chelation therapy for patients with thalassemia major and other refractory anemias requiring regular transfusions depended almost entirely on one drug, deferoxamine. The drug has dramatically increased survival in patients with thalassemia major in countries where it is readily

Although iron chelation therapy with deferoxamine (DFO) results in improved life expectancy of patients with thalassemia, compliance with parenteral DFO treatment is unsatisfactory, underlining the need for alternative drugs and innovative ways of drug administration. We examined the chelating potential of pyridoxal isonicotinoyl hydrazone (PIH) analogs, alone or in combination with DFO, using hypertansfused rats with labeled hepatocellular iron stores and cultured iron-loaded rat heart cells. Our in vivo studies using 2 representative PIH analogs, 108-o and 109-o, have shown that PIH analogs given orally are 2.6 to 2.8 times more effective in mobilizing hepatocellular iron in rats, on a weight-per-weight basis, than parenteral DFO administered intraperitoneally. The combined effect of DFO and 108-o on hepatocellular iron excretion was additive, and response at a dose range of 25 to 200 mg/kg was linear. In vitro studies in heart cells showed that DFO was more effective in heart cell iron mobilization than all PIH analogs studied. Response to joint chelation with DFO and PIH analogs was similar to an increase in the equivalent molar dose of DFO alone, rather than the sum of the separate effects of the PIH analog and DFO. This finding was most likely the result of iron transfer from PIH analogs to DFO, a conclusion supported directly by iron-shuttle experiments using fluorescent DFO. These findings provide a rationale for the combined, simultaneous use of iron-chelating drugs and may have useful, practical implications for designing novel strategies of iron chelation therapy.

Although the beneficial effects of deferoxamine (DFO) on iron-associated morbidity and mortality are well documented, the role of deferiprone (L1) in the management of transfusional iron overload is controversial. This debate involves not only the question of efficacy but also of safety, with particular emphasis on the risk of a paradoxical aggravation of iron toxicity by L1. We used the iron-loaded gerbil model introduced by Carthew et al to compare the chelating efficacy of L1, DFO, or both in two gerbil strains treated by means of weekly iron-dextran injections: Psammomys obesus and pathogen-free Mongolian gerbils (Meriones unguiculatus). The difference between the high mortality and advanced hepatocellular necrosis observed in iron-loaded P obesus and the absence of mortality and limited morbidity encountered in pathogen-free Mongolian gerbils is most likely explained by the prevention of coincidental laboratory infections in the latter group. Iron-chelating treatment in all experimental groups resulted in a significant decrease in hepatic iron concentrations and normalization of mitochondrial respiratory enzyme activities, with combined L1 and DFO treatment being the most efficient, followed, in decreasing order, by DFO and L1 as single-drug treatments. Judged by tissue iron concentrations, mitochondrial enzyme activity, and hepatic histology, we could find no evidence of a paradoxical aggravation of iron toxicity by L1 in either of the two series of studies. Although these data appear to be reassuring, the present controversy related to the role of L1 in the development of hepatic cirrhosis should be eventually settled by clinical studies evaluating the effects of long-term iron-chelating treatment.

In chronic anemias associated with iron overload, iron chelation therapy is the only method available for preventing early death caused mainly by myocardial and hepatic iron toxicity. Although desferrioxamine (DFO) has been available for the treatment of transfusional iron overload since the early 1960s, the era of modern and effective iron chelation therapy started only 20 years ago with the introduction of subcutaneous DFO infusions by portable pumps. Today, long-term DFO therapy is an integral part of the management of thalassemia and other transfusion-dependent anemias, with a major impact on well-being and survival. However, the high cost and rigorous requirements of DFO therapy and the significant toxicity of deferiprone underline the need for the continued development of new and improved orally effective iron chelators. In recent years, more than 1000 candidate compounds have been screened in animal models. These efforts have led to the identification of several interesting compounds, a few of which may be of possible clinical usefulness. The present review covers some of the most outstanding of these compounds, including deferiprone (L1), pyridoxal isonicotinoyl hydrazone (PIH), the polyanionic amines, the substituted polyaza compounds and bishydroxyphenyl tiazole. The introduction of these promising new chelators and the evolution of improved strategies of iron chelation therapy require a better understanding of the pathophysiology of iron toxicity and of the mechanisms of action of iron chelating drugs.

Nontransferrin-bound iron (NTBI) appears in the serum of individuals with iron overload and in a variety of other pathologic conditions. Because NTBI constitutes a labile form of iron, it might underlie some of the biologic damage associated with iron overload. We have developed a simple method for NTBI determination, which operates in a 96-well enzyme-linked immunosorbent assay format with sensitivity comparable to that of previous assays. A weak ligand, oxalic acid, mobilizes the NTBI and mediates its transfer to the iron chelator deferoxamine (DFO) immobilized on the plate. The amount of DFO-bound iron, originating from NTBI, is quantitatively revealed in a fluorescence plate reader by the fluorescent metallosensor calcein. No NTBI is found in normal sera because transferrin-bound iron is not detected in the assay. Thalassemic sera contained NTBI in 80% of the cases (range, 0.9-12.8 μmol/L). In patients given intravenous infusions of DFO, NTBI initially became undetectable due to the presence of DFO in the sera, but reappeared in 55% of the cases within an hour of cessation of the DFO infusion. This apparent rebound was attributable to the loss of DFO from the circulation and the possibility that a major portion of NTBI was not mobilized by DFO. NTBI was also found in patients with end-stage renal disease who were treated for anemia with intravenous iron supplements and in patients with hereditary hemochromatosis, at respective frequencies of 22% and 69%. The availability of a simple assay for monitoring NTBI could provide a useful index of iron status during chelation and supplementation treatments.

Human erythroid precursors grown in culture possess membrane receptors that bind and internalize acid isoferritin. These receptors are regulated by the iron status of the cell, implying that ferritin iron uptake may represent a normal physiologic pathway. The present studies describe the fate of internalized ferritin, the mechanisms involved in the release of its iron, and the recognition of this iron by the cell. Normal human erythroid precursors were grown in a 2-phase liquid culture that supports the proliferation, differentiation, and maturation of erythroid precursors. At the stage of polychromatic normoblasts, cells were briefly incubated with 59Fe- and/or125I-labeled acid isoferritin and chased. The125I-labeled ferritin protein was rapidly degraded and only 50% of the label remained in intact ferritin protein after 3 to 4 hours. In parallel, 59Fe decreased in ferritin and increased in hemoglobin. Extracellular holoferritin uptake elevated the cellular labile iron pool (LIP) and reduced iron regulatory protein (IRP) activity; this was inhibited by leupeptin or chloroquine. Extracellular apoferritin taken up by the cell functioned as an iron scavenger: it decreased the level of cellular LIP and increased IRP activity. We suggest that the iron from extracellular is metabolized in a similar fashion by developing erythroid cells as is intracellular ferritin. Following its uptake, extracellular ferritin iron is released by proteolytic degradation of the protein shell in an acid compartment. The released iron induces an increase in the cellular LIP and participates in heme synthesis and in intracellular iron regulatory pathways.

Because mitochondrial inner membrane respiratory complexes are important targets of iron toxicity, we used iron-loaded rat heart cells in culture to study the beneficial effect on mitochondrial enzymes of the iron chelators deferoxamine (DFO) and deferiprone (L1) and of antioxidants and reducing agents (ascorbate and α-tocopherol). Reduced nicotinamide adenine dinucleotide–cytochrome c oxidoreductase (complex I-III) and succinate dehydrogenase were the most-sensitive indicators of iron toxicity and cardioprotective effect. Although at concentrations below 0.3 mmol/L the iron-mobilizing effect of L1 was less than that of DFO, both were equally effective in protecting or restoring mitochondrial respiratory enzyme activity. At 1.0 mmol/L, L1 toxicity was manifested in respiratory enzyme inhibition, whereas DFO had no such effect. Ascorbate (0.057 to 5.7 mmol/L) had a mild cardioprotective effect at the highest concentration only, in association with decreased cellular iron uptake. By contrast, α-tocopherol (0.023 mmol/L) completely inhibited mitochondrial iron toxicity without affecting iron uptake or release, and irrespective of whether it was used before, during, or after in vitro iron loading. These observations illustrate the usefulness and limitations of iron chelators and other agents used for preventing iron toxicity to the heart and other vital organs, and they underline the need for exploring in more detail the effects of these agents in the clinical setting. (J Lab Clin Med 1999;133:179-88)

In thalassemia, iron overload is the joint outcome of excessive iron absorption and transfusional siderosis. While iron absorption is limited by a physiologic ceiling of about 3 mg/d, plasma iron turnover in thalassemia may be 10 to 15 times normal, caused by the wasteful, ineffective erythropoiesis of an enormously expanded erythroid marrow. This outpouring of catabolic iron exceeds the iron-binding capacity of transferrin and appears in plasma as non-transferrin-plasma iron (NTPI). The toxicity of NTPI is much higher than of transferrin-iron as judged by its ability to promote hydroxyl radical formation resulting in peroxidative damage to membrane lipids and proteins. In the heart, this results in impaired function of the mitochrondrial respiratory chain and abnormal energy metabolism manifested clinically in fatal hemosiderotic cardiomyopathy. Ascorbate increases the efficacy of iron chelators by expanding the intracellular chelatable iron pool, but, at suboptimal concentrations is a pro-oxidant, enhancing the catalytic effect of iron in free radical formation. NTPI is removed by i.v. DFO in a biphasic manner and reappears rapidly upon cessation of DFO, lending support to the continuous, rather than intermittent, use of chelators. Unlike DFO and other hexadentate chelators, bidentate chelators such as L1 may produce incomplete intermediate iron complexes at suboptimal drug concentrations.

A major consideration in the selection of new and improved iron chelators for clinical use is preferential interaction with the most toxic iron compartment. We describe the biologic properties of a new synthetic hexadentate iron chelator (IRC011) that is a substituted polyaza compound. Unlike deferoxamine (DF ), the polyaza structure of IRC011 does not contain any readily hydrolyzable covalent bonds and is anticipated to resist in vivo biotransformation. In the present studies, the ability of IRC011 to remove radioiron from iron-loaded heart cells in vitro was similar to DF, with a decrease to 20.0 ± 0.4% and 19.7 ± 0.5% of initial values after 24 hours of incubation with 0.3 mmol/L of DF or IRC011, respectively. The in vivo interaction of IRC011 with specific iron stores was studied in hypertransfused rats using selective labeling of reticuloendothelial (RE) iron stores with 59Fe-heat-denatured red blood cells (DRBCs) and of hepatocellular stores with 59Fe-ferritin. The pattern of radioiron excretion with IRC011 was quite different from that with DF. Although with both compounds, hepatocellular iron excretion was through the bile, whereas RE iron excretion was mainly in the urine, the magnitude of these effects was quite different. After the administration of a single parenteral dose of 200 mg/kg representing a 53% higher iron-binding capacity for IRC011 compared with DF, 48-hour urinary excretion of RE iron with IRC011 was 22.8% ± 1.1% (% of total body 59Fe), but only 6.0% ± 3.6% with DF. By contrast, the corresponding biliary excretion of hepatocellular radioiron was 14.2% ± 3.2% with DF, but only 0.7% ± 0.3% with IRC011. Thus, the new iron chelator IRC011 is distinguished from DF by the following features: (1) a higher affinity to Fe(III), (2) anticipated resistance to in vivo catabolism, (3) preferential interaction with RE iron derived from RBC breakdown, and (4) selective renal excretion. Because RBC breakdown is the most likely source of the toxic nontranferrin plasma iron, IRC011 may be a useful iron chelator for protecting vital organs from peroxidative damage.

Endoscopic gastrointestinal workup fails to establish the cause of iron deficiency anemia (IDA) in a substantial proportion of patients. In patients referred for hematologic evaluation with unexplained or refractory IDA, screening for celiac disease, autoimmune gastritis, Helicobacter pylori, and hereditary forms of IDA is recommended. About 4% to 6% of patients with obscure refractory IDA have celiac disease, and autoimmune gastritis is encountered in 20% to 27% of patients. Stratification by age cohorts in autoimmune gastritis implies a disease presenting as IDA many years before the establishment of clinical cobalamin deficiency. Over 50% of patients with unexplained refractory IDA have active H pylori infection and, after excluding all other causes of IDA, 64% to 75% of such patients are permanently cured by H pylori eradication. In young patients with a history suggestive of hereditary iron deficiency with serum ferritin higher than expected for IDA, mutations involving iron trafficking and regulation should be considered. Recognition of the respective roles of H pylori, autoimmune gastritis, celiac disease, and genetic defects in the pathogenesis of iron deficiency should have a strong impact on the current diagnostic workup and management of unexplained, or refractory, IDA.

The role of iron in anthracycline toxicity was studied in rats in vivo in intact animals and in vitro in heart cell cultures. In animals treated with 8 mg/kg doxorubicin, iron loading resulted in severe weight loss and a twofold increase in rate of mortality. Studies in cultured heart cells aimed at defining the subcellular target of interaction between iron and anthracycline toxicity showed no evidence of anthracycline-induced damage to sarcolemmal thiolic enzymes represented by 5′-nucleotidase and only a limited increase in lysosomal fragility as monitored by an increase in β-hexosaminidase activity in cell homogenates and its release into the culture medium. By contrast, doxorubicin treatment resulted in a marked inhibition of mitochondrial function as monitored by a decrease in carbon 14-labeled palmitate utilization, to 33% ± 4% of controls, and prior iron loading resulted in a further decrease in palmitate utilization, to 18% ± 3% of controls. Conversely, iron-chelation treatment by either deferoxamine or deferiprone (L1) eliminated the harmful effects of iron loading and resulted in a partial inhibition of doxorubicin toxicity in both normal and iron-loaded cells. Our studies represent the first demonstration in intact animals of the potentiation of anthracycline toxicity by iron overload. They also indicate that mitochondria represent an important target of combined iron-anthracycline toxicity. These observations provide new insights into the mechanism of anthracycline cardiotoxicity and may be useful in developing better strategies for tumor therapy.

The use of anthracycline antineoplastic drugs is limited by a cumulative, dose-dependent toxicity to the heart. Of the cellular organelles proposed as possible primary sites of anthracycline toxicity, the mitochondrial membrane appears to be most likely target. Cardiolipin, a major phospholipid component of the inner mitochondrial membrane is rich in polyunsaturated fatty acids and is particularly susceptible to peroxidative injury by harmful radicals produced by redox cycling of anthracyclines. This, in turn, leads to the inactivation of key enzymes in the mitochondrial respiratory chain. Since the formation of free radicals is catalyzed by iron through the Haber-Weiss reaction, it was hypothesized that iron depletion by deferoxamine (DFO) may limit anthracycline cardiotoxicity. Recent studies indicate that iron-loading aggravates doxorubicin cardiotoxicity by enhancing mitochondrial damage, and this can be prevented by prior DFO treatment. Although these observations are intriguing, further studies are required to show that the cardioprotective effects of DFO do not interfere with the therapeutic, antitumoral action of anthracyclines.

Introduction The abnormalities in iron metabolism associated with megaloblastic anemia are rapidly reversed by B(12) therapy in pernicious anemia (PA). Although non-tranferrin-bound plasma iron (NTBI) was previously shown to be associated with severe iron overload, its origin is unknown. Methods and results Four patients with PA were studied before and after B(12) treatment. NTBI was measured by a fluorescence-based one-step assay. All patients had very high transferrin saturation, NTBI values ranging from 1.1 to 2.6 micromol/l and normal serum ferritins. B(12) treatment resulted in the disappearance of NTBI and normalization of transferrin saturation within 22-42 h. Conclusions The prompt disappearance of NTBI following B(12) therapy implicates catabolic iron derived from ineffective erythropoiesis as the major source of NTBI in untreated PA and possibly in thalassemia major and sideroblastic anemia. Our findings offer further insight into the pathogenesis of NTBI in diseases associated with abnormal erythropoiesis.

Recognition of the central role of iron in the generation of toxic, oxygen-derived species through the Haber-Weiss reaction, the ability of desferrioxamine (DFX) to prevent the damage associated with free radical generation in reperfusion injury, and its inhibitory effect on cell proliferation by inactivation of the iron dependent enzyme ribonucleotide reductase, resulted in an increasing number of studies exploring the novel therapeutic applications of iron chelating drugs: (a) Animal models of reperfusion injury have shown that DFX is able to decrease post-anoxic damage to the brain and heart as manifested in decreased infarct size and improved functional recovery. Iron chelators may be particularly useful in improving the preservation of organs intended for transplantation such as the heart, lung or kidney. (b) Anthracycline cardiotoxicity is aggravated by iron and inhibited by iron chelators. Because the mechanism of its antineoplastic effect differs from its cardiotoxic effect, it is possible to inhibit anthracycline cardiotoxicity without interfering with therapeutic efficacy. In vivo and in vitro animal studies have yielded encouraging results but much additional experimental work is still required before iron chelating therapy may be advocated for use in patients on anthracycline therapy. (c) Cell proliferation can be inhibited by iron chelators through the reversible inhibition of ribonucleotide reductase, a rate-limiting enzyme in DNA synthesis. This may be exploited for the treatment of malignant disease, and preliminary studies have already shown that DFX in combination with multidrug chemotherapy is effective in controlling neuroblastoma and other tumours. However, the contribution of DF to the overall clinical effect is unclear. Prospective controlled clinical studies are required in order to establish whether the antiproliferative, or cell synchronizing properties of DFX may be of practical usefulness in the control of malignant disease. (d) Control of protozoal infection: Experimental in vivo and in vitro models have shown that malarial infection may be inhibited by iron chelating therapy. This useful effect of DFX and other iron chelators is most probably related to ribonucleotide reductase inhibition. Clinical studies of asymptomatic P. falciparum malaria and of cerebral malaria have shown both an accelerated rate of parasite clearance and earlier recovery from coma. These observations lend new meaning to the term 'nutritional immunity' and open new channels for exploring the possibility of controlling infection by means of selective intracellular iron deprivation. Experimental models for studying the effect of iron chelators on other intracellular pathogens such as Toxoplasma gondii, Chlamydia psittaci, or Mycobacterium tuberculosis should be established.(ABSTRACT TRUNCATED AT 400 WORDS)

In view of the profound functional and structural abnormalities shown in our previous studies in cultured, iron-loaded rat heart cells, we have examined the ability of the orally effective iron chelators dimethyl-3-hydroxypyrid-4-one (DMHP or L1) and diethyl-3-hydroxy-pyrid- 4-one (DEHP or CP94) and of deferoxamine (DF) to reverse the damage caused by iron loading to heart cell organelles. At a concentration of 1.0 mmol/L, all three iron chelators were equally efficient in removing iron and restoring the activity of the thiolic sarcolemmal enzymes 5′- nucleotidase and Na,K,ATPase. However, at 0.1 mmol/L DMHP and DEHP were less effective than DF both in their iron-mobilizing effect and in promoting thiolic enzyme recovery. The superior efficiency of DF at low concentrations illustrates the advantage of the hexadentate chelating action of DF as compared with bidentate chelators such as DMHP and DEHP requiring a 3 to 1 molar ratio to iron for optimal effect. In contrast to its beneficial effect on sarcolemmal enzyme activity, iron chelation was unable to reverse the increase in beta-hexosaminidase activity caused by abnormal lysosomal fragility. Our study demonstrates for the first time that iron-induced peroxidative damage to the myocardial cell is associated with a marked loss of Na,K,ATPase activity, an enzyme with a major role in the maintenance of cellular resting potential. The timing of this damage and the restoration of Na,K,ATPase function by iron-chelating treatment suggest a cause-and-effect relationship between the observed injury to the sarcolemmal enzyme and the reversible electrophysiologic abnormalities observed in the same heart culture system in our previous studies.

Repeated blood transfusions lead to the appearance of plasma non-transferrin-bound iron species (NTBI) that distribute to hepatocytes, endocrine tissues and the heart. Morbidity and mortality reflects this distribution, with heart failure remaining the leading cause of death in inadequately treated thalassaemia major (TM) patients.

Iron overload in MDS is the joint outcome of multiple blood transfusions and inappropriately increased iron absorption associated with ineffective erythropoiesis. Experience gained in hereditary iron-loading anemias indicates that the long-term consequences of iron toxicity are preventable and reversible by effective iron chelation therapy (ICT). With the introduction of orally effective iron chelators that are easy to take and suitable for use in elderly patients, there is increasing interest in offering ICT to patients with MDS. Ideally, evidence supporting the beneficial effects of iron chelation in MDS should rest on proof of improved life expectancy and in exceptional cases, reversal of myocardial disease. However, such evidence is presently unavailable.

The redox cycling of anthracyclines promotes the formation of free radicals which are believed to play a central role in their cardiotoxicity. A number of observations indicate that the mechanism of the antineoplastic effect of anthracyclines is independent of their cardiotoxic effect and that it may be possible to prevent toxicity without interfering with therapeutic effect. Iron plays an important role in anthracycline toxicity by promoting the conversion of superoxide into highly toxic hydroxyl radicals through the Haber-Weiss reaction. Conversely, iron deprivation by its high-affinity binding to iron chelating compounds may inhibit anthracycline toxicity by interfering with free radical formation. ICRF-187, a bispiperazonedione which is hydrolyzed intracellularly into a bidentate chelator resembling EDTA, is able to decrease adriamycin-induced free hydroxyl radical formation and to prevent the development of clinical cardiac toxicity in patients receiving long-term anthracycline therapy. Our studies in rat heart cell cultures have shown that iron overload aggravates anthracycline toxicity and that this interaction can be prevented by prior iron chelating treatment. Since iron overload caused by multiple blood transfusions and bone marrow failure is a common condition in patients requiring anthracycline therapy, these observations may have significant clinical implications to the prevention of anthracycline cardiotoxicity.

Increased sensitivity to warfarin anticoagulation is usually attributed to liver disease, vitamin K deficiency, or drug interactions. We describe a patient with unexplained sensitivity to warfarin and mildly elevated prostate-specific antigen levels in whom subsequent developments indicated that warfarin sensitivity was the first manifestation of occult prostatic cancer. A review of all published cases of coagulopathy associated with cancer of the prostate shows that, unlike other solid tumors with secondary disseminated intravascular coagulation (DIC), in prostate cancer increased bleeding is more common than thrombotic phenomena. Chronic DIC due to occult prostate cancer should be included in the differential diagnosis of excessive prothrombin time prolongation in patients receiving anticoagulants.

Osteoporosis is a frequent problem in disorders characterized by iron overload, such as the thalassemias and hereditary hemochromatosis. The exact role of iron in the development of osteoporosis in these disorders is not established. To define the effect of iron excess in bone, we generated an iron-overloaded mouse by injecting iron dextran at 2 doses into C57/BL6 mice for 2 months. Compared with the placebo group, iron-overloaded mice exhibited dose-dependent increased tissue iron content, changes in bone composition, and trabecular and cortical thinning of bone accompanied by increased bone resorption. Iron-overloaded mice had increased reactive oxygen species and elevated serum tumor necrosis factor-α and interleukin-6 concentrations that correlated with severity of iron overload. Treatment of iron-overloaded mice with the antioxidant N-acetyl-L-cysteine prevented the development of trabecular but not cortical bone abnormalities. This is the first study to demonstrate that iron overload in mice results in increased bone resorption and oxidative stress, leading to changes in bone microarchitecture and material properties and thus bone loss.