Iron chelation therapy for iron loaded patients

Biosynthesis of iron-chelating terramides A-C and their role in Aspergillus terreus infection

Fungal natural products from various species often feature hydroxamic acid motifs that have the ability to chelate iron. These compounds have an array of medicinally and ecologically relevant activities. Through genome mining, gene deletion in the host Aspergillus terreus, and heterologous expression experiments, this study has revealed that a nonribosomal peptide synthetase (NRPS) TamA and a specialized cytochrome P450 monooxygenase TamB catalyze the sequential biosynthetic reactions in the formation of terramides A-C, a series of diketopiperazines (DKPs) with hydroxamic acid motifs. Feeding experiments showed that TamB catalyzes an unprecedented di-hydroxylation of the amide nitrogens in the diketopiperazine core. This tailoring reaction led to the formation of two bidentate iron-binding sites per molecule with an unusual iron-binding stoichiometry. The structure of the terramide A-Fe complex was characterized by liquid chromatography-mass spectrometry (LC-MS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and electron paramagnetic resonance spectroscopy (EPR). Antimicrobial assays showed that the iron-binding motifs are crucial for the activity against bacteria and fungi. Murine infection experiments indicated that terramide production is crucial for the virulence of A. terreus and could be a potential antifungal drug target.

Molecular Recognition Based Iron Removal from Human Plasma with Imprinted Membranes

The aim of this study is to prepare ion-imprinted poly(2-hydroxyethyl methacrylate) (HEMA) based membranes which can be used for the selective removal of Fe3+ ions from Fe3+-overdosed human plasma. N-methacryloyl-(L)-glutamic acid (MAGA) was chosen as the ioncomplexing monomer. In the first step, Fe3+ was complexed with MAGA and then, the Fe3+-imprinted poly(HEMA-MAGA) membranes were prepared by UV-initiated photo-polymerization of HEMA and MAGA-Fe3+ complex in the presence of an initiator (benzoyl peroxide). After that, the template (i.e., Fe3+ ions) was removed by using 0.1 M EDTA solution at room temperature. The specific surface area of the Fe3+-imprinted poly(HEMA-MAGA) membranes was found to be 49.2 m2/g and the swelling ratio was 92%. According to the elemental analysis results, the polymeric membranes contained 145.7 μmol MAGA/g polymer. The maximum adsorption capacity was 164.2 μmol Fe3+/g membrane. The relative selectivity coefficients of ion-imprinted membranes for Fe3+/Zn2+ and Fe3+/Cr3+ were 12.6 and 62.5 times greater than the non-imprinted matrix, respectively. The Fe3+-imprinted poly(HEMA-MAGA) membranes could be used many times without decreasing their Fe3+ adsorption capacities significantly.

Host-directed therapies for infectious diseases: current status, recent progress, and future prospects

Despite extensive global efforts in the fight against killer infectious diseases, they still cause one in four deaths worldwide and are important causes of long-term functional disability arising from tissue damage. The continuing epidemics of tuberculosis, HIV, malaria, and influenza, and the emergence of novel zoonotic pathogens represent major clinical management challenges worldwide. Newer approaches to improving treatment outcomes are needed to reduce the high morbidity and mortality caused by infectious diseases. Recent insights into pathogen–host interactions, pathogenesis, inflammatory pathways, and the host's innate and acquired immune responses are leading to identification and development of a wide range of host-directed therapies with different mechanisms of action. Host-directed therapeutic strategies are now becoming viable adjuncts to standard antimicrobial treatment. Host-directed therapies include commonly used drugs for non-communicable diseases with good safety profiles, immunomodulatory agents, biologics (eg monoclonal antibodies), nutritional products, and cellular therapy using the patient's own immune or bone marrow mesenchymal stromal cells. We discuss clinically relevant examples of progress in identifying host-directed therapies as adjunct treatment options for bacterial, viral, and parasitic infectious diseases.

Catechuic acid and ethyl 2,4,5-trihydroxybenzoate from D-glucose

Synthesis of catechuic acid (1) and ethyl 2,4,5-trihydroxybenzoate (2) from D-glucose-derived beta-ketoester is described. The polyhydroxylated beta-ketoester obtained from the hydrolysis of sugar beta-ketoester 3 was subjected to an aldol-type condensation to get 4 that on enolization, dehydration, and hydrogenation afforded ethyl 2,4,5-trihydroxybenzoate (2). On the other hand, hydrogenation of aldol product 4 afforded polyhydroxylated keto-carbasugar 6, which on mild acid treatment and ester hydrolysis in basic media led to catechuic acid 1. Intermediate 4 is co-related to 3-dehydroshikimic acid, a biochemical intermediate from D-glucose in the synthesis of pro-catechuic acid.

New chelate-forming polymer microspheres carrying dyes as chelators for iron overload

Dye-incorporated [poly(EGDMA-HEMA)] microspheres were investigated as a new chelate-forming polymer for iron overload. Poly(EGDMA-HEMA) microspheres, in the size range of 150-200 microm, were produced by a modified suspension polymerization of EGDMA and HEMA. The reactive dye-ligands (i.e. Cibacron Blue F3GA, Alkali Blue 6B and Congo Red) were covalently incorporated to the microspheres. The maximum dye incorporations were 16.5 micromol Cibacron Blue F3GA g(-1), 23.7 micromol Alkali Blue 6B g(-1), and 14.5 micromol Congo Red g(-1). The maximum Fe(III) adsorptions on the dye-incorporated microspheres from aqueous solutions containing different amounts of Fe(III) ions were 51.0, 37.3, and 25.1 mg g(-1) for the Cibacron Blue F3GA, Alkali Blue 6B, and Congo Red carrying microspheres, respectively. The maximum Fe(III) adsorptions were observed at pH 4.0 in all cases. Fe(III) removal from human plasma was also investigated. The maximum adsorption capacities of Fe(III) ions from human plasma for Cibacron Blue F3GA, Alkali Blue 6B, and Congo Red, were of 12.0, 7.5, and 3.8 mg g(-1) polymer, respectively. It was observed that Fe(III) could be repeatedly adsorbed and desorbed without significant loss in adsorption capacity.

[Post-transfusion hemochromatosis. Results of a study carried out in Blood Transfusion Centers. Analysis of 15 cases treated with subcutaneous perfusion of Desferal. Working group "Transfusion Techniques and Therapeutics"]

Post-transfusional iron overload is a real problem for doctors in charge of transfusions, as shown by the survey we led in twenty French blood banks. Deferoxamine remains the most efficient chelator, but can be prescribed only in a parenteral way. It is now proved that continuous infusions, intravenous or subcutaneous, are preferable to intermittent injections as far as iron excretion is concerned. In our study, we selected 15 polytransfused patients for dysmyelopoiesis. 13 cases were analysed by measuring the serum ferritin level. A clear decrease was noted, as well as a relative normalization of serum alanine amino transferases. However, if this treatment is effective and well tolerated, the problem is that it obviously requires the patient's compliance. It seems important to us to optimize prevention and treatment of post-transfusional iron overload through a consensus.

Prooxidant action of desferrioxamine: enhancement of alkaline phosphatase inactivation by interaction with ascorbate system

Desferrioxamine (DFO) nearly doubles alkaline phosphatase oxidative inactivation by the ascorbate system. The effect is dependent on ascorbate and desferrioxamine concentrations, exhibiting in both cases a saturation mechanism. Conversion of desferrioxamine to ferrioxamine abolishes the prooxidant action. Desferrioxamine also increases ascorbate-dependent oxygen consumption and nitroblue tetrazolium reduction. Superoxide dismutase, which blocks the desferrioxamine enhancing effect on enzyme inactivation, markedly slows down nitroblue tetrazolium reduction as well as oxygen consumption by ascorbate plus desferrioxamine, while it fails to protect against the ascorbate system alone. Therefore, in the presence of desferrioxamine, the metal-catalyzed ascorbate autooxidation becomes superoxide-dependent and thus inhibitable by superoxide dismutase. Catalase, peroxidase, and ascorbate oxidase protect alkaline phosphatase from inactivation by both ascorbate and ascorbate-desferrioxamine systems. Hemin shields the enzyme from ascorbate plus DFO attack but not from ascorbate alone. In air-saturated solution, desferrioxamine seems to mediate one electron transfer from ascorbate to oxygen, generating superoxide anions, which can either trigger a Fenton reaction or produce desferal nitroxide radicals. In the absence of oxygen, ascorbate alone is ineffective, but the ascorbate plus desferrioxamine system still inactivates the enzyme; catalase, peroxidase, and ascorbate oxidase, but not superoxide dismutase, afford protection.

Iron chelation by pyridoxal isonicotinoyl hydrazone and analogues in hepatocytes in culture

Pyridoxal isonicotinoyl hydrazone (PIH) and several analogues were synthesized and assessed in the rat hepatocyte culture for their potential in iron chelation therapy. Pyridoxal isonicotinoyl hydrazone and pyridoxal benzoyl hydrazone were as effective as desferrioxamine (DFO) in reducing both net uptake of rat transferrin-59Fe and incorporation into ferritin by hepatocytes. Dialysis studies showed that this was due to a cellular action and not to the extracellular chelation of transferrin-bound 59Fe. The analogues of PIH were more effective in mobilization studies than PIH and DFO, releasing more 59Fe from ferritin as well as from the stroma-mitochondrial membranes in hepatocytes prelabelled using transferrin-59Fe. Chelator action was dependent on incubation time, concentration, temperature and lipophilicity. Pyridoxal benzoyl hydrazone, the most effective iron chelator, was also the most lipophilic, suggesting that access to cellular iron compartments as well as iron-binding affinity is important in effective iron chelation.

Iron deficiency and iron overload

An up to date review of our knowledge of human iron metabolism is given including problems of iron balance, internal transport, and intracellular mechanisms. Current knowledge of the iron proteins is summarized and this background is used in discussing the pathophysiology of iron deficiency and overload, together with the internal derangements such as sideroblastic anemia which form much of the clinical practice associated with disorders of iron metabolism. The therapeutic approach to these problems will be described.

Pyridoxal complexes as potential chelating agents for oral therapy in transfusional iron overload

Iron chelation therapy for patients maintained on a regular transfusion regime is at present best carried out by means of daily infusions of desferrioxamine (Hussain et al 1977; Pippard et al 1978) but this is onerous for the patient and has social and economic disadvantages. Many recent attempts to provide more effective drugs for iron chelation have been summarized by Jacobs (1979) and increasing attention is now being paid to the possibility of oral iron chelation therapy. Hoy et al (1979) showed that when isonicotinic acid hydrazide (INH) and pyridoxal are mixed in equimolar amounts a hydrazone is formed which chelates iron, and oral administration of this compound to rats results in an eightfold increase in faecal iron excretion. It is effective on repeated administration (Cikrt et al 1980), the main route of iron excretion being through the bile. Long term studies in the rat have not been successful in reducing the iron load of test animals and this appears to be related both to their high dietary iron content and instability of the hydrazone. Its effective shelf life at room temperature is no longer than one month and this is a considerable disadvantage from a therapeutic point of view. Pyridoxal is known to form a Schiff base with many amino acids and its reactivity has led us to examine complexes of pyridoxal with a number of substances in an attempt to find an alternative iron chelator of greater stability than the INH complex and of comparable effectiveness on oral administration. The screening procedures used were the effects on Chang cell iron metabolism (White et al 1976) and on iron excretion in the rat (Hoy et al 1979).

Ferric ion sequestering agents: kinetics of iron release from ferritin to catechoylamides

The removal of ferric ion from the iron storage protein ferritin to synthetic catechoylamide sequestering agents has been studied using visible spectroscopy at 487 nm. One ligand which has been investigated in detail is N,N',N' ',-tris(2,3-dihydroxy-5-sulfobenzoyl)-1,5,10-triazadecane (3,4-LICAMS), which octahedrally coordinates the metal ion via six phenolic oxygens. For some related catechoylamide chelates, the percentage of iron removed after 6 h has been determined. These ligands incorporate various modifications, either on the catechol moiety or on the backbone structure of the ligand. Mobilization of iron by the catechoylamide ligands alone results in very slow exchange, and virtually no iron removal after 6 h. In contrast, addition of ascorbic acid to the reaction mixture facilitates iron exchange, with the release of 7% of the available iron in the same time span. Variation of the initial rate with ascorbic acid concentration results in Michaelis-Menten kinetics with Km = 1.7 . 10(-3) M and a maximal rate of 1.28 . 10(-7) M . min-1. The ascorbic acid-mediated rate was not affected by changing the catechoylamide ligand concentration, and was only slightly affected by variation of the ligand employed. These data are consistent with a multistep process which includes diffusion of a reductant into the ferritin inner core, reduction and possible chelation of the ferrous ion, diffusion out of the protein shell, and subsequent iron exchange with the catechoylamide molecule.

Disorders of iron metabolism

Although iron in minute amounts is necessary for the metabolism of most cells, it produces damage if present in excess. Clinical tools for the evaluation of iron stores include serum iron concentration, transferrin saturation, deferoxamine test, Prussian blue stains of liver and marrow, and serum ferritin concentration. Serum ferritin concentration is an excellent screening test for iron deficiency or excessive iron stores. If excessive iron stores is diagnosed, the iron should be removed with phlebotomies or chelation therapy.