Iron chelation,quo vadis?

Orally bioavailable chelators for transfusional iron overload have been sought since the introduction of deferoxamine (Desferal) in 1962. Despite tremendous efforts, to date, only deferiprone (Ferriprox) and deferasirox (Exjade) have successfully reached the market, reflecting the difficulty to combine oral activity and safety. Owing to the risk of failure, few new oral chelators can be expected in the future for the treatment of transfusional iron overload. As iron is involved in many disease processes, deferiprone and deferasirox have been proposed to be potentially useful in a variety of indications not characterized by general iron overload. Although it may be possible to obtain clinical benefit from current compounds, more selective chelators tailored to the particular target are needed for successful intervention in these indications.     

Chelation in metal intoxication—Principles and paradigms

The present review provides an update of the general principles for the investigation and use of chelating agents in the treatment of intoxications by metals. The clinical use of the old chelators EDTA (ethylenediamine tetraacetate) and BAL (2,3-dimercaptopropanol) is now limited due to the inconvenience of parenteral administration, their own toxicity and tendency to increase the neurotoxicity of several metals. The hydrophilic dithiol chelators DMSA (meso-2,3-dimercaptosuccinic acid) and DMPS (2,3-dimercapto-propanesulphonate) are less toxic and more efficient than BAL in the clinical treatment of heavy metal poisoning, and available as capsules for oral use. In copper overload, DMSA appears to be a potent antidote, although d-penicillamine is still widely used. In the chelation of iron, the thiols are inefficient, since iron has higher affinity for ligands with nitrogen and oxygen, but the new oral iron antidotes deferiprone and desferasirox have entered into the clinical arena. Comparisons of these agents and deferoxamine infusions are in progress. General principles for research and development of new chelators are briefly outlined in this review.     

Post-transfusional iron overload in the haemoglobinopathies

In this report, we review the recent advances in evaluation and treatment of transfusional iron overload (IO). Results of the French thalassaemia registry are described. According to the disease, thalassaemia major or sickle cell anaemia, mechanisms and toxicity of iron overload, knowledge about IO long-term outcome and chelation treatment results, respective value of IO markers, differ. The recent tools evaluating organ specific IO and the diversification of iron chelator agents make possible to individualize chelation therapy in clinical practice. The severity of IO and the level of transfusional iron intake, the preferential localization of IO (heart/liver) as well as the tolerance and adherence profiles of the patient can now be taken into account. Introduction of cardiac magnetic resonance imaging for the quantification of myocardial iron and use of oral chelators have already been reported as decreasing the cardiac mortality rate related to IO in thalassaemia major patients. Long-term observation of patients under oral chelators will show if morbidity is also improving via a more continuous control of toxic iron and/or a better accessibility to cellular iron pools.     

Antimalarial iron chelator, FBS0701, shows asexual and gametocyte Plasmodium falciparum activity and single oral dose cure in a murine malaria model

Iron chelators for the treatment of malaria have proven therapeutic activity in vitro and in vivo in both humans and mice, but their clinical use is limited by the unsuitable absorption and pharmacokinetic properties of the few available iron chelators. FBS0701, (S)3"-(HO)-desazadesferrithiocin-polyether [DADFT-PE], is an oral iron chelator currently in Phase 2 human studies for the treatment of transfusional iron overload. The drug has very favorable absorption and pharmacokinetic properties allowing for once-daily use to deplete circulating free iron with human plasma concentrations in the high μM range. Here we show that FBS0701 has inhibition concentration 50% (IC(50)) of 6 μM for Plasmodium falciparum in contrast to the IC(50) for deferiprone and deferoxamine at 15 and 30 μM respectively. In combination, FBS0701 interfered with artemisinin parasite inhibition and was additive with chloroquine or quinine parasite inhibition. FBS0701 killed early stage P. falciparum gametocytes. In the P. berghei Thompson suppression test, a single dose of 100 mg/kg reduced day three parasitemia and prolonged survival, but did not cure mice. Treatment with a single oral dose of 100 mg/kg one day after infection with 10 million lethal P. yoelii 17XL cured all the mice. Pretreatment of mice with a single oral dose of FBS0701 seven days or one day before resulted in the cure of some mice. Plasma exposures and other pharmacokinetics parameters in mice of the 100 mg/kg dose are similar to a 3 mg/kg dose in humans. In conclusion, FBS0701 demonstrates a single oral dose cure of the lethal P. yoelii model. Significantly, this effect persists after the chelator has cleared from plasma. FBS0701 was demonstrated to remove labile iron from erythrocytes as well as enter erythrocytes to chelate iron. FBS0701 may find clinically utility as monotherapy, a malarial prophylactic or, more likely, in combination with other antimalarials.     

Hierro e infección fúngica invasiva

Iron is an essential factor for both the growth and virulence of most of microorganisms. As a part of the innate (or nutritional) immune system, mammals have developed different mechanisms to store and transport this element in order to limit free iron bioavailability. To survive in this hostile environment, pathogenic fungi have specific uptake systems for host iron sources, one of the most important of which is based on the synthesis of siderophores-soluble, low-molecular-mass, high-affinity iron chelators. The increase in free iron that results from iron-overload conditions is a well-established risk factor for invasive fungal infection (IFI) such as mucormycosis or aspergillosis. Therefore, iron chelation may be an appealing therapeutic option for these infections. Nevertheless, deferoxamine –the first approved iron chelator– paradoxically increases the incidence of IFI, as it serves as a xeno-siderophore to Mucorales. On the contrary, the new oral iron chelators (deferiprone and deferasirox) have shown to exert a deleterious effect on fungal growth both in vitro and in animal models. The present review focuses on the role of iron metabolism in the pathogenesis of IFI and summarises the preclinical data, as well as the limited clinical experience so far, in the use of new iron chelators as treatment for mucormycosis and invasive aspergillosis.     

Disorders associated with systemic or local iron overload: from pathophysiology to clinical practice

In healthy subjects, the rate of dietary iron absorption, as well as the amount and distribution of body iron are tightly controlled by hepcidin, the iron regulatory hormone. Disruption of systemic iron homeostasis leads to pathological conditions, ranging from anemias caused by iron deficiency or defective iron traffic, to iron overload (hemochromatosis). Other iron-related disorders are caused by misregulation of cellular iron metabolism, which results in local accumulation of the metal in mitochondria. Brain iron overload is observed in neurodegenerative disorders. Secondary hemochromatosis develops as a complication of another disease. For example, repeated blood transfusions, a standard treatment of various anemias characterized by ineffective erythropoiesis, promote transfusional siderosis, while chronic liver diseases are often associated with mild to moderate secondary iron overload. In this critical review, we discuss pathophysiological and clinical aspects of all types of iron metabolism disorders (265 references).     

Objectives and Methods of Iron Chelation Therapy

Recent developments in the understanding of the molecular control of iron homeostasis provided novel insights into the mechanisms responsible for normal iron balance. However in chronic anemias associated with iron overload, such mechanisms are no longer sufficient to offer protection from iron toxicity, and iron chelating therapy is the only method available for preventing early death caused mainly by myocardial and hepatic damage. Today, long-term deferoxamine (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. Within recent years more than one thousand candidate compounds have been screened in animal models. The most outstanding of these compounds include deferiprone (L1); pyridoxal isonicotinoyl hydrazone (PIH) and; bishydroxy- phenyl thiazole. Deferiprone has been used extensively as a substitute for DFO in clinical trials involving hundreds of patients. However, L1 treatment alone fails to achieve a negative iron balance in a substantial proportion of subjects. Deferiprone is less effective than DFO and its potential hepatotoxicity is an issue of current controversy. A new orally effective iron chelator should not necessarily be regarded as one displacing the presently accepted and highly effective parenteral drug DFO. Rather, it could be employed to extend the scope of iron chelating strategies in a manner analogous with the combined use of medications in the management of other conditions such as hypertension or diabetes. Coadministration or alternating use of DFO and a suitable oral chelator may allow a decrease in dosage of both drugs and improve compliance by decreasing the demand on tedious parenteral drug administration. Combined use of DFO and L1 has already been shown to result in successful depletion of iron stores in patients previously failing to respond to single drug therapy, and to lead to improved compliance with treatment. It may also result in a “shuttle effect” between weak intracellular chelators and powerful extracellular chelators or exploit the entero-hepatic cycle to promote fecal iron excretion. All of these innovative ways of chelator usage are now awaiting evaluation in experimental models and in the clinical setting.     

Effects of Iron Overload on Ascorbic Acid Metabolism

Studies of the ascorbic acid status in two subjects with idiopathic haemochromatosis and in 12 with transfusional siderosis showed that all had decreased levels of white cell ascorbic acid. The urinary excretion of ascorbic acid was also diminished in those subjects in whom such measurements were made. The administration of ascorbic acid was followed by only a small rise in the urinary ascorbic acid output, while the oxalic acid levels (measured in two subjects) showed a significant rise. These findings resemble those described in siderotic Bantu, and support the thesis that increased iron stores lead to irreversible oxidation of some of the available ascorbic acid.     

Therapeutic potential of induced iron depletion using iron chelators in Covid-19

Ferritin, which includes twenty-four light and heavy chains in varying proportions in different tissues, is primarily responsible for maintaining the body's iron metabolism. Its normal value is between 10 and 200 ngmL^?1 in men and between 30 and 300 ngmL^?1 in women. Iron is delivered to the tissue via them, and they act as immunomodulators, signaling molecules, and inflammatory markers. When ferritin level exceeds 1000 µgL^-1, the patient is categorized as having hyperferritinemia. Iron chelators such as deferiprone, deferirox, and deferoxamine are currently FDA approved to treat iron overload. The inflammation cascade and poor prognosis of COVID-19 may be attributed to high ferritin levels. Critically ill patients can benefit from deferasirox, an iron chelator administered orally at 20–40 mgkg^?1 once daily, as well as intravenous deferoxamine at 1000 mg initially followed by 500 mg every 4 to 12 h. It can be combined with monoclonal antibodies, antioxidants, corticosteroids, and lactoferrin to make iron chelation therapy effective for COVID-19 victims. In this article, we analyze the antiviral and antifibrotic activity of iron chelators, thereby promoting iron depletion therapy as a potentially innovative treatment strategy for COVID-19.     

Effective chelation of iron in beta thalassaemia with the oral chelator 1,2-dimethyl-3-hydroxypyrid-4-one.

The main iron chelator used for transfusional iron overload is desferrioxamine, which is expensive, has toxic side effects, and has to be given subcutaneously. An orally active iron chelator is therefore required. The effects of oral 1,2-dimethyl-3-hydroxypyrid-4-one on urinary iron excretion were studied in eight patients who had received multiple transfusions: four had myelodysplasia and four beta thalassaemia major. Different daily doses of the drug up to 100 mg/kg/day, alone or in combination with ascorbic acid, were used. In three patients with thalassaemia the effect of the drug was compared with that of subcutaneous desferrioxamine at the same daily dose. In all eight patients a single dose of oral 1,2-dimethyl-3-hydroxypyrid-4-one resulted in substantial urinary iron excretion, mainly in the first 12 hours. Urinary iron excretion increased with the dose and with the degree of iron loading of the patient. Giving two or three divided doses over 24 hours resulted in higher urinary iron excretion than a single dose of the same amount over the same time. In most patients coadministration of oral ascorbic acid further increased urinary iron excretion. 1,2-Dimethyl-3-hydroxypyrid-4-one caused similar iron excretion to that achieved with subcutaneous desferrioxamine at a comparable dose. In some cases the iron excretion was sufficiently high (maximum 99 mg/day) to suggest that a negative iron balance could be easily achieved with these protocols in patients receiving regular transfusions. No evidence of toxicity was observed on thorough clinical examination or haematological and biochemical testing in any of the patients. None of the patients had any symptoms that could be ascribed to the drug. These results suggest that the oral chelator 1,2-dimethyl-3-hydroxypyrid-4-one is as effective as subcutaneous desferrioxamine in increasing urinary iron excretion in patients loaded with iron. Its cheap synthesis, oral activity, and lack of obvious toxicity at effective doses suggest that it should be developed quickly and thoroughly tested for the management of transfusional iron overload.     

Current status in iron chelation in hemoglobinopathies

Although blood transfusions are important for patients with hemoglobinopathies, chronic transfusions inevitably lead to iron overload as humans cannot actively remove excess iron. The cumulative effects of iron overload lead to significant morbidity and mortality, if untreated. Desferrioxamine (DFO) is the reference-standard iron chelator whose safety and efficacy profile has been established through many years of clinical use. DFO side effects are acceptable and manageable however the prolonged subcutaneous infusion regimen of 5-7 days per week is very demanding and results in poor adherence to therapy. Deferiprone (Ferriprox, L1) is a bidentate molecule, orally administrable three-times/day, licensed in Europe and in other regions but in the USA and Canada, for the treatment of iron overload in patients for whom DFO therapy is contraindicated or inadequate. Preliminary evidences suggest that Deferiprone may be more effective than DFO in chelating cardiac iron. The side effects include gastrointestinal symptoms, liver dysfunction, joint pain, neutropenia and agranulocytosis. A weekly assessment of white blood cell counts is recommended because of the risk of agranulocytosis. Deferasirox is a new, convenient, once-daily oral iron chelator that has demonstrated in various clinical trials good efficacy and acceptable safety profile in adult and pediatric patients affected by transfusion-dependent thalassemia major and by different chronic anemias (SCD, BDA, MDS). The long half-life of Deferasirox (16-18 hours) provides sustained 24 hr iron chelation coverage. The efficacy and safety profile have been evaluated in more than 1000 patients in clinical trials allowing FDA registration. Patient satisfaction with Deferasirox was superior than with DFO therapy.     

Characterization of two siderophores produced by Bacillus megaterium: A preliminary investigation into their potential as therapeutic agents

BackgroundMicroorganisms produce siderophores in order to scavenge iron from the environment and this study focuses on the characterization of the two siderophores secreted by Bacillus megaterium. The general biological properties and pharmacokinetics following oral application of these compounds are reported.MethodsUnder optimized culture conditions, the siderophores were harvested, purified by chromatography and identified using LC-MS and NMR. Two dihydroxamate siderophores were isolated, schizokinen (MW = 420) and schizokinen imide (MW = 402).ResultsBoth compounds demonstrate strong antioxidant activity and were found to be relatively nontoxic to both human hepatocellular carcinoma (Huh7) and peripheral blood mononuclear cells. The siderophores possess a strong affinity for iron(III) and decrease the levels of the labile iron pool (LIP) in iron-loaded cells in a concentration-dependent manner. Schizokinen, was detected as both the free siderophore and the iron complex in the plasma and urine of rats after oral gavage.ConclusionsHowever, the bioavailability was low and thus schizokinen, like deferoxamine, has no potential as an orally active iron chelator for the treatment of systemic iron overload.General significanceBy virtue of the high affinity of schizokinen for tribasic metals, this siderophore does have considerable potential for the chelation of gallium(III) and the development of clinical diagnostic reagents.     

Three most common nonsynonymous UGT1A6*2 polymorphisms (Thr181Ala,Arg184Serand Ser7Ala) and therapeutic response to deferiprone in β-thalassemia major patients

Deferiprone is used as a chelation agent in chronic iron overload in β-thalassemia patients. Patients on deferiprone therapy show variable response to this drug in terms of reduction in iron overload as well as adverse drug reactions (ADRs). The pharmacogenetic studies on deferiprone have not carried out in patients with blood disorders in India. Therefore, the present study was carried out to evaluate the three most common nonsynonymous UGT1A6 polymorphisms Thr181Ala (541 A/G), Arg184Ser (552 A/C) and Ser7Ala (19 T/G) and therapeutic response to deferiprone in β-thalassemia major patients. Two hundred and eighty six (286) β-thalassemia major patients were involved in the study. Serum ferritin levels were estimated periodically to assess the status of the iron overload and the patients were grouped into responders and non-responders depending on the ferritin levels. The UGT1A6*2 polymorphisms were detected by PCR-RFLP methods. The association between the genotypes and outcome as well as ADRs was evaluated by Open EPI software. A significant difference was observed in the genotypic distribution of UGT1A6*2 Thr181Ala polymorphism in responders and non-responders. However, there was no difference in the genotypic distribution between patients with and without ADRs. As far as the UGT1A6*2 Arg184Ser polymorphism is concerned, no significant difference was observed between responders and non-responders. Further, evaluating the association of UGT1A6*2 Ser7Ala polymorphism with drug response, there was no significant difference in the genotypic distribution between responders and non-responders. However, there was a significant difference between responders with and without ADRs and non-responders with and without ADRs. In addition to this haplotype analysis was also carried out. However, we did not find any specific haplotype to be significantly associated with the deferiprone response in β-thalassemia major patients.     

Hepatic iron deposition in human disease and animal models

Iron deposition occurs in parenchymal cells of the liver in two major defects in human subjects (i) in primary iron overload (genetic haemochromatosis) and (ii) secondary to anaemias in which erythropolesis is increased (thalassaemia). Transfusional iron overload results in excessive storage primarily in cells of the reticule endothelial system. The storage patterns in these situations are quite characteristic. Excessive iron storage, particularly in parenchymal cells eventually results in fibrosis and cirrhosis. There is no animal model or iron overload which completely mimics genetics haemochromatosis but dietary iron loading with carbonyl iron or ferrocene does produce excessive parenchymal iron stores in the rat. Such models have been used to study iron toxicity and the action of iron chelators in the effective removal of excessive iron stores.     

Hereditary haemochromatosis: only 1% of adult HFEC282Y homozygotes in South Wales have a clinical diagnosis of iron overload

In northern Europe, about 90% of patients with hereditary haemochromatosis (HH) are homozygous for a single mutation (C282Y) of the HFEgene and approximately 1 in 150 people in the general population carries this genotype. However, the clinical significance of HFE mutations remains uncertain, as is the proportion of people homozygous for C282Y who will develop clinical symptoms leading to a diagnosis of HH. A systematic review of patients with HH over a 2-year period within a defined UK region has revealed that only 1.2% of adult C282Y homozygotes have been diagnosed with iron overload and received treatment. In those in whom body iron load could be estimated, only 51% has more than 4 g iron (the diagnostic threshold for iron overload).     

Early detection of genetic hemochromatosis: should all young adults be offered the genetic test?

Genetic hemochromatosis (GH) is a late-onset, autosomal recessive disorder. The majority of those at risk from iron overload and its clinical consequences may be detected by a simple genetic test. Furthermore, treatment by phlebotomy, if instituted early, removes excess iron and prevents the complications of iron overload which include arthralgia, diabetes, and cirrhosis of the liver. GH seems to be an obvious candidate for inclusion in national screening programs. However, important questions remain concerning the proportion of individuals with the high-risk genotype who eventually show clinical manifestations of iron overload and the significance of heterozygosity for haemochromatosis in terms of morbidity. Until these questions are resolved, the introduction of widespread genetic screening cannot be justified.     

The study of iron mobilisation from transferrin using alpha-ketohydroxy heteroaromatic chelators

A group of heteroaromatic chelators with an alpha-ketohydroxy binding site have been tested for their ability to mobilise iron from transferrin in vitro. When these chelators were mixed with iron-saturated transferrin at physiological pH, biphasic reactions were observed. The alpha-ketohydroxy heteroaromatic chelators were found to cause substantial iron removal compared to other known chelators. These findings suggest that these chelators may have an important role in the study of iron metabolism and a possible clinical use in the treatment of transfusional iron overload in thalassaemia, and other diseases of iron imbalance.     

Deferoxamine mesylate enhances virulence of community-associated methicillin resistant Staphylococcus aureus

Staphylococcus aureus is a leading cause of bacterial infections. Strains of community-associated methicillin-resistant S. aureus (CA-MRSA), such as USA300, display enhanced virulence and fitness. Patients suffering from iron overload diseases often undergo iron chelation therapy with deferoxamine mesylate (DFO). Here, we show that USA300 uses this drug to acquire iron. We further demonstrate that mice administered DFO I.P., versus those not administered DFO, had significantly higher bacterial burden in livers and kidneys after I.V. challenge with USA300, associated with increased abscess formation and tissue destruction. The virulence of USA300 mutants defective for DFO uptake was not affected by DFO treatment.     

Liver iron depletion and toxicity of the iron chelator Deferiprone (L, CP20) in the guinea pig

The use of the iron chelator deferiprone (L, CP20, 1,2-dimethyl-3-hydroxypyrid-4-one) for the treatment of diseases of iron overload and other disorders is problematic and requires further evaluation. In this study the efficacy, toxicity and mechanism of action of orally administered L were investigated in the guinea pig using the carbonyl iron model of iron overload. In an acute trial, depletion of liver non-heme iron in drug-treated guinea pigs (normal iron status) was maximal (approximately 50% of control) after a single oral dose of L1 of 200 mg kg, suggesting a limited chelatable pool in normal tissue. There was no apparent toxicity up to 600 mg kg. In each of two sub-acute trials, normal and iron-loaded animals were fed L (300 mg kg day) or placebo for six days. Final mortalities were 12/20 (L) and 0/20 (placebo). Symptoms included weakness, weight loss and eye discharge. Iron-loaded as well as normal guinea pigs were affected, indicating that at this drug level iron loading was not protective. In a chronic trial guinea pigs received L (50 mg kg day) or placebo for six days per week over eight months. Liver non-heme iron was reduced in animals iron-loaded prior to the trial. The increase in a wave latency (electroretinogram), the foci of hepatic, myocardial and musculo-skeletal necrosis, and the decrease in white blood cells in the drug-treated/normal diet group even at the low dose of 50 mg kg day suggests that L may be unsuitable for the treatment of diseases which do not involve Fe overload. However, the low level of pathology in animals treated with iron prior to the trial suggests that even a small degree of iron overload (two-fold after eight months) is protective at this drug level. We conclude that the relationship between drug dose and iron status is critical in avoiding toxicity and must be monitored rigorously as cellular iron is depleted.